Lymphocyte proliferative responses to human immunodeficiency virus antigens in vitro

The role of CD4+ T cells in tumor and chronic viral immune responses

Immunotherapies are mainly aimed to promote a CD8+ T cell response rather than a CD4+ T cell response as cytotoxic T lymphocytes (CTLs) can directly kill target cells. Recently, CD4+ T cells have received more attention due to their diverse roles in tumors and chronic viral infections. In antitumor and antichronic viral responses, CD4+ T cells relay help signals through dendritic cells to indirectly regulate CD8+ T cell response, interact with B cells or macrophages to indirectly modulate humoral immunity or macrophage polarization, and inhibit tumor blood vessel formation. Additionally, CD4+ T cells can also exhibit direct cytotoxicity toward target cells. However, regulatory T cells exhibit immunosuppression and CD4+ T cells become exhausted, which promote tumor progression and chronic viral persistence. Finally, we also outline immunotherapies based on CD4+ T cells, including adoptive cell transfer, vaccines, and immune checkpoint blockade. Overall, this review summarizes diverse roles of CD4+ T cells in the antitumor or protumor and chronic viral responses, and also highlights the immunotherapies based on CD4+ T cells, giving a better understanding of their roles in tumors and chronic viral infections.

Comparison of the Biological Basis for Non-HIV Transmission to HIV-Exposed Seronegative Individuals, Disease Non-Progression in HIV Long-Term Non-Progressors and Elite Controllers

HIV-exposed seronegative individuals (HESIs) are a small fraction of persons who are multiply exposed to human immunodeficiency virus (HIV), but do not exhibit serological or clinical evidence of HIV infection. In other words, they are groups of people maintaining an uninfected status for a long time, even after being exposed to HIV several times. The long-term non-progressors (LTNPs), on the other hand, are a group of HIV-infected individuals (approx. 5%) who remain clinically and immunologically stable for an extended number of years without combination antiretroviral therapy (cART). Meanwhile, elite controllers are comprise a much lower number (0.5%) of HIV-infected persons who spontaneously and durably control viremia to below levels of detection for at least 12 months, even when using the most sensitive assays, such as polymerase chain reaction (PCR) in the absence of cART. Despite the fact that there is no universal agreement regarding the mechanisms by which these groups of individuals are able to control HIV infection and/or disease progression, there is a general consensus that the mechanisms of protection are multifaceted and include genetic, immunological as well as viral factors. In this review, we analyze and compare the biological factors responsible for the control of HIV in these unique groups of individuals.

Changes in the cellular microRNA profile by the intracellular expression of HIV-1 Tat regulator: A potential mechanism for resistance to apoptosis and impaired proliferation in HIV-1 infected CD4+ T cells

HIV-1 induces changes in the miRNA expression profile of infected CD4+ T cells that could improve viral replication. HIV-1 regulator Tat modifies the cellular gene expression and has been appointed as an RNA silencing suppressor. Tat is a 101-residue protein codified by two exons that regulates the elongation of viral transcripts. The first exon of Tat (amino acids 1–72) forms the transcriptionally active protein Tat72, but the presence of the second exon (amino acids 73–101) results in a more competent regulatory protein (Tat101) with additional functions. Intracellular, full-length Tat101 induces functional and morphological changes in CD4+ T cells that contribute to HIV-1 pathogenesis such as delay in T-cell proliferation and protection against FasL-mediated apoptosis. But the precise mechanism by which Tat produces these changes remains unknown. We analyzed how the stable expression of intracellular Tat101 and Tat72 modified the miRNA expression profile in Jurkat cells and if this correlated with changes in apoptotic pathways and cell cycle observed in Tat-expressing cells. Specifically, the enhanced expression of hsa-miR-21 and hsa-miR-222 in Jurkat-Tat101 cells was associated with the reduced expression of target mRNAs encoding proteins related to apoptosis and cell cycle such as PTEN, PDCD4 and CDKN1B. We developed Jurkat cells with stable expression of hsa-miR-21 or hsa-miR-222 and observed a similar pattern to Jurkat-Tat101 in resistance to FasL-mediated apoptosis, cell cycle arrest in G₂/M and altered cell morphology. Consequently, upregulation of hsa-miR-21 and hsa-miR-222 by Tat may contribute to protect against apoptosis and to anergy observed in HIV-infected CD4+ T cells.

Mechanisms of Virologic Control and Clinical Characteristics of HIV+ Elite/Viremic Controllers

Human immunodeficiency virus type 1 (HIV-1) disease is pandemic, with approximately 36 million infected individuals world-wide. For the vast majority of these individuals, untreated HIV eventually causes CD4+ T cell depletion and profound immunodeficiency, resulting in morbidity and mortality. But for a remarkable few (0.2 to 0.5 percent), termed elite controllers (ECs), viral loads (VLs) remain suppressed to undetectable levels (< 50 copies/ml) and peripheral CD4+ T cell counts remain high (200 to 1000/μl), all in the absence of antiretroviral therapy (ART). Viremic controllers (VCs) are a similar but larger subset of HIV-1 infected individuals who have the ability to suppress their VLs to low levels. These patients have been intensively studied over the last 10 years in order to determine how they are able to naturally control HIV in the absence of medications, and a variety of mechanisms have been proposed. Defective HIV does not explain the clinical status of most ECs/VCs; rather these individuals appear to somehow control HIV infection, through immune or other unknown mechanisms. Over time, many ECs and VCs eventually lose the ability to control HIV, leading to CD4+ T cell depletion and immunologic dysfunction in the absence of ART. Elucidating novel mechanisms of HIV control in this group of patients will be an important step in understanding HIV infection. This will extend our knowledge of HIV-host interaction and may pave the way for the development of new therapeutic approaches and advance the cure agenda.

Distinctive features of CD4+ T cell dysfunction in chronic viral infections

PURPOSE OF REVIEW

To describe recent advances in the understanding of virus-specific CD4 T cell dysfunction in chronic viral infections, with an emphasis on HIV disease. We highlight features that are distinctive for CD4 T cells, as opposed to their CD8 T cell counterparts.

RECENT FINDINGS

CD4 T cell activation and differentiation are tightly controlled. Regulation of these processes depends on the context of initial encounter of the naïve CD4 T cell with the cognate antigen and on ongoing external cues to the antigen-experienced CD4 T cell, in particular the inflammatory environment, which is prominent in HIV infection. Virus-specific CD4 T cell dysfunction results from a combination of an exhaustion program and skewing in T helper lineage differentiation which impact function. The CD4 and CD8 T cell exhaustion programs present similarities and distinct features. The sets of inhibitory coreceptors expression differ, although programmed-death 1 (PD-1) and T cell immunoglobulin mucin-3 (Tim-3) are upregulated on both HIV-specific CD4 and CD8 T cells, cytotoxic T-lymphocyte antigen 4 (CTLA-4) is largely specific to CD4 T cells, whereas 2B4 and CD160 are biased toward CD8 T cells.

SUMMARY

Understanding the molecular basis of HIV-specific CD4 T cell exhaustion and identifying key differences with CD8 T cell impairment will be critical to design effective therapeutic and preventive immunotherapies against HIV.

Differential Gag-specific polyfunctional T cell maturation patterns in HIV-1 elite controllers

A small fraction of HIV-infected individuals (<1%), referred to as elite controllers (EC), are able to maintain undetectable viral loads indefinitely without treatment. The role of the maturational phenotype of T cells in the control of HIV infection in these individuals is not well described. We compared the maturational and functional phenotypes of Gag-specific CD4 and CD8 T cells from EC, who maintain undetectable viral loads without treatment; relative controllers (RC), who maintain viral loads of <1,000 copies/ml without treatment; and noncontrollers (NC), who fail to control viral replication. EC maintained higher frequencies of HIV-specific CD4 T cells, less mature polyfunctional Gag-specific CD4 T cells (CD27(+) CD57(-) CD45RO(+)), and Gag-specific polyfunctional CD4 T cells than those observed in NC. In EC, the frequency of polyfunctional Gag-specific CD8 T cells was higher than that observed in RC and NC. RC had a similar functional phenotype to that observed in NC, despite consistently lower viral loads. Finally, we found a direct correlation between the frequency of Gag-specific CD27(+) CD57(-) CD45RO(+) CD4(+) T cells and the frequency of mature HIV-specific CD8 T cells. Altogether, our data suggest that immature Gag-specific interleukin-2 (IL-2)-producing CD4(+) T cells may play an important role in spontaneous control of HIV viremia by effectively supporting HIV-specific CD8 T lymphocytes. This difference appears to differentiate EC from RC.

HIV-specific CD4 T cells and immune control of viral replication

PURPOSE OF REVIEW

To understand the role of HIV-specific CD4 T cells in viral control and highlight recent progress in the field.

RECENT FINDINGS

HIV-specific CD4 T cells show higher functional avidity in elite controllers than in patients with progressive infection. There is an attrition of the HIV-specific CD4 T-cell population in the digestive mucosa of antiretroviral therapy (ART)-treated patients that contrasts with robust responses in individuals with spontaneous viral control. Secretion of the cytokine IL-21, by HIV-specific CD4 T cells, is associated with disease control and enhances the capacity of HIV-specific CD8 T cells to suppress viral replication. Studies of the PD-1, IL-10, and Tim-3 pathways provided insight into mechanisms of HIV-specific CD4 T-cell exhaustion and new evidence that manipulation of these networks may restore immune functions. Robust, polyfunctional CD4 T-cell responses can be elicited with novel HIV and simian immunodeficiency virus (SIV) vaccines.

SUMMARY

These observations show that HIV-specific CD4 T-cell responses are different in elite controllers and individuals with progressive disease. Evidence suggests that HIV-specific CD4 T cells will be an important component of an effective HIV vaccine and significant efforts need to be made to further our understanding of HIV-specific CD4 T-cell functions in different body compartments.

SIV antigen immunization induces transient antigen-specific T cell responses and selectively activates viral replication in draining lymph nodes in retroviral suppressed rhesus macaques

Background

HIV infection causes a qualitative and quantitative loss of CD4⁺ T cell immunity. The institution of anti-retroviral therapy (ART) restores CD4⁺ T cell responses to many pathogens, but HIV-specific responses remain deficient. Similarly, therapeutic immunization with HIV antigens of chronically infected, ART treated subjects results in poor induction of HIV-specific CD4 responses. In this study, we used a macaque model of ART treatment during chronic infection to study the virologic consequences of SIV antigen stimulation in lymph nodes early after immunization. Rhesus CMV (RhCMV) seropositive, Mamu A*01 positive rhesus macaques were chronically infected with SIVmac251 and treated with ART. The immune and viral responses to SIV gag and RhCMV pp65 antigen immunization in draining lymph nodes and peripheral blood were analyzed. Animals were immunized on contralateral sides with SIV gag and RhCMV pp65 encoding plasmids, which allowed lymph nodes draining each antigen to be obtained at the same time from the same animal for direct comparison.

Results

We observed that both SIV and RhCMV immunizations stimulated transient antigen-specific T cell responses in draining lymph nodes. The RhCMV-specific responses were potent and sustained (50 days post-immunization) in the periphery, while the SIV-specific responses were transient and extinguished quickly. The SIV antigen stimulation selectively induced transient SIV replication in draining lymph nodes.

Conclusions

The data are consistent with a model whereby viral replication in response to SIV antigen stimulation limits the generation of SIV antigen-specific responses and suggests a potential mechanism for the early loss and poor HIV-specific CD4⁺ T cell response observed in HIV-infected individuals.

Identification of HIV-1 epitopes that induce the synthesis of a R5 HIV-1 suppression factor by human CD4+ T cells isolated from HIV-1 immunized hu-PBL SCID mice

We have previously reported that immunization of the severe combined immunodeficiency (SCID) mice reconstituted with human peripheral blood mononuclear cells (PBMC) (hu-PBL-SCID mice) with inactivated human immunodeficiency virus type-1 (HIV-1)-pulsed-autologous dendritic cells (HIV-DC) elicits HIV-1-reactive CD4(+) T cells that produce an as yet to be defined novel soluble factor in vitro with anti-viral properties against CCR5 tropic (R5) HIV-1 infection. These findings led us to perform studies designed to identify the lineage of the cell that synthesizes such a factor in vivo and define the epitopes of HIV-1 protein that have specificity for the induction of such anti-viral factor. Results of our studies show that this property is a function of CD4(+) but not CD8(+) T cells. Human CD4(+) T cells were thus recovered from the HIV-DC-immunized hu-PBL-SCID mice and were re-stimulated in vitro by co-culture for 2 days with autologous adherent PBMC as antigen presenting cells, APC previously pulsed with inactivated HIV in IL-2-containing medium to expand HIV-1-reactive CD4(+) T cells. Aliquots of these re-stimulated CD4(+) T cells were then co-cultured with similar APC's that were previously pulsed with 10 microg/ml of a panel of HIV peptides for an additional 2 days, and their culture supernatants were examined for the production of both the R5 HIV-1 suppression factor and IFN-gamma. The data presented herein show that the HIV-1 primed CD4(+) T cells produced the R5 suppression factor in response to a wide variety of HIV-1 gag, env, pol, nef or vif peptides, depending on the donor of the CD4(+) T cells. Simultaneous production of human interferon (IFN)-gamma was observed in some cases. These results indicate that human CD4(+) T cells in PBMC of HIV-1 naive donors have a wide variety of HIV-1 epitope-specific CD4(+) T cell precursors that are capable of producing the R5 HIV-1 suppression factor upon DC-based vaccination with whole inactivated HIV-1.

Analysis of the immune responses in chimpanzees infected with HIV type 1 isolates

The mechanisms of resistance to AIDS development in HIV-1-infected chimpanzees have remained elusive. Unique among chimpanzees naturally or experimentally infected with HIV, several animals of the Yerkes cohort have progressed to clinical AIDS with selection of isolates showing increased pathogenicity for chimpanzees. We compared progressors vs. nonprogressors among the HIV-infected chimpanzees that made up this cohort, eight of which have been infected with HIV-1 for over 14 years. The additional two progressors were infected de novo with chimpanzee-pathogenic HIV, rapidly leading to a progressor status. Nonprogressors were characterized by normal CD4(+) T cell counts and the absence of detectable viremia. In contrast, progressor chimpanzees had relatively high plasma viral loads associated with a dramatic loss of CD4(+) T cells. The analysis of immune responses showed a similar amplitude and breadth of ELISPOT T cell responses in both groups. HIV-specific proliferative responses were, however, absent in the progressor animals, which also exhibited increased levels of immune activation characterized by elevated levels of the circulating chemokines IP-10 and MCP-1. Of interest was the conservation of potent NK cell activity in all animals, potentially contributing to the extended symptom-free survival of progressor animals. Modest anti-HIV antibody titers were detectable in the nonprogressor group, but these antibodies exhibited good neutralizing activity. In progressors, however, two sets of data were noted: in animals that gradually selected for pathogenic isolates, or that were superinfected, very high neutralizing antibody titers were observed, although none to the pathogenic HIV. In contrast, two animals infected de novo with chimpanzee pathogenic HIV failed to mount an extensive humoral response and both failed to develop neutralizing antibodies to the virus. Taken together, pathogenic HIV infection in chimpanzees is associated with rapid loss of CD4(+) T cells and proliferative responses as well as higher levels of immune activation.

Human immunodeficiency virus (HIV)-2-specific T lymphocyte proliferative responses in HIV-2-infected and in HIV-2-exposed but uninfected individuals in Guinea-Bissau

Human immunodeficiency virus (HIV)-2-specific T lymphocyte proliferative responses were determined in cultures of peripheral blood mononuclear cells from HIV-2-exposed uninfected individuals, HIV-2-infected individuals and HIV-negative controls in Guinea-Bissau. Increased HIV-2-specific T lymphocyte proliferative responses were detected in both groups compared to HIV-negative controls (healthy HIV-uninfected individuals without known exposure to an HIV-infected person); five out of 29 of the HIV-2-exposed uninfected and half (16 of 32) of the HIV-2-infected individuals had stimulation indexes >2, compared to one out of 49 of the HIV-negative controls (P = 0.003 and P < 0.0001, respectively). The exposed uninfected individuals had reactivity to a HIV-2 V3-peptide corresponding to amino acids 311-326 of the envelope glycoprotein, while the HIV-2-infected people reacted mainly to HIV-2 whole viral lysate. Thus, this study demonstrates a high degree of HIV-2-specific T helper cell activity, as measured by lymphocyte proliferation, in HIV-2-exposed uninfected individuals as well as in HIV-2-infected subjects. These immune responses could be important for resistance to the infection and for the control of established infection and, thus, play a role in the lower transmission and progression of HIV-2 compared to HIV-1.

Limited durability of viral control following treated acute HIV infection

BACKGROUND

Early treatment of acute HIV infection with highly active antiretroviral therapy, followed by supervised treatment interruption (STI), has been associated with at least transient control of viremia. However, the durability of such control remains unclear. Here we present longitudinal follow-up of a single-arm, open-label study assessing the impact of STI in the setting of acute HIV-1 infection.

METHODS AND FINDINGS

Fourteen patients were treated during acute HIV-1 infection and subsequently subjected to an STI protocol that required retreatment if viral load exceeded 50,000 RNA copies/ml plasma or remained above 5,000 copies/ml for more than three consecutive weeks. Eleven of 14 (79%) patients were able to achieve viral loads of less than 5,000 RNA copies/ml for at least 90 d following one, two, or three interruptions of treatment. However, a gradual increase in viremia and decline in CD4+ T cell counts was observed in most individuals. By an intention-to-treat analysis, eight (57%), six (43%), and three (21%) of 14 patients achieved a maximal period of control of 180, 360, and 720 d, respectively, despite augmentation of HIV-specific CD4+ and CD8+ T cell responses. The magnitude of HIV-1-specific cellular immune responses before treatment interruption did not predict duration of viremia control. The small sample size and lack of concurrent untreated controls preclude assessment of possible clinical benefit despite failure to control viremia by study criteria.

CONCLUSIONS

These data indicate that despite initial control of viremia, durable viral control to less than 5,000 RNA copies/ml plasma in patients following treated acute HIV-1 infection occurs infrequently. Determination of whether early treatment leads to overall clinical benefit will require a larger and randomized clinical trial. These data may be relevant to current efforts to develop an HIV-1 vaccine designed to retard disease progression rather than prevent infection since they indicate that durable maintenance of low-level viremia may be difficult to achieve.

Comprehensive analysis of human immunodeficiency virus type 1-specific CD4 responses reveals marked immunodominance of gag and nef and the presence of broadly recognized peptides

Increasing evidence suggests that human immunodeficiency virus type 1 (HIV-1)-specific CD4 T-cell responses contribute to effective immune control of HIV-1 infection. However, the breadths and specificities of these responses have not been defined. We screened fresh CD8-depleted peripheral blood mononuclear cells (PBMC) from 36 subjects at different stages of HIV-1 infection for virus-specific CD4 responses by gamma interferon enzyme-linked immunospot assay, using 410 overlapping peptides spanning all HIV-1 proteins (based on the clade B consensus sequence). HIV-1-specific CD4 responses were identified in 30 of the 36 individuals studied, with the strongest and broadest responses detected in persons treated in acute infection who underwent treatment interruption. In individuals with identified responses, the total number of recognized HIV-1 peptides ranged from 1 to 36 (median, 7) and the total magnitude of responses ranged from 80 to >14,600 (median, 990) spot-forming cells/10(6) CD8-depleted PBMC. Neither the total magnitude nor the number of responses correlated with viremia. The most frequent and robust responses were directed against epitopes within the Gag and Nef proteins. Peptides targeted by >/=25% of individuals were then tested for binding to a panel of common HLA-DR molecules. All bound broadly to at least four of the eight alleles tested, and two bound to all of the HLA-DR molecules studied. Fine mapping and HLA restriction of the responses against four of these peptides showed a combination of clustering of epitopes and promiscuous presentation of the same epitopes by different HLA class II alleles. These findings have implications for the design of immunotherapeutic strategies and for testing candidate HIV vaccines.

Long-term persistence of vaccination and HAART to human immunodeficiency virus (HIV)

The aim of this study was to monitor the immune responses in HIV-infected patients previously immunized with gp160 or DNA vaccines to analyze whether the introduction of highly active antiretroviral treatment (HAART) would affect the persistence of immunity. The immune responses were evaluated in patients who had participated in randomized trials of therapeutic vaccination. Immunization in conjunction with antiretroviral therapy was effective in inducing HIV-specific T-cell responses. Therapeutic immunizations with recombinant gp160 had a modest effect on CD4-cell counts, the treatment alone lead to a transient clinical benefit in the form of an improved survival after two years of immunization. Immunizations with HIV DNA during HAART treatment permitted persistence or development of innate (NK), CD4+ and/or CD8+ immune responses. HIV specific T-helper cell responses induced by immunization with gp160 were maintained at high levels up to 7 years after the last injection. Cells with HIV-specific interferon-gamma (IFN-gamma) production were retained or increased in long-term HAART treated patients. The impact of a single structured therapy interruption (STI) was analyzed in a small group of patients showing no obvious increase or decrease in the HIV-specific immune response during or after STI. The possibility to induce very long-term strong and persistent immune responses in HIV-infected individuals raises hopes that vaccination preceding therapy interruption might prolong the symptom-free period without HAART.

Discordance between frequency of human immunodeficiency virus type 1 (HIV-1)-specific gamma interferon-producing CD4(+) T cells and HIV-1-specific lymphoproliferation in HIV-1-infected subjects with active viral replication

One hallmark of uncontrolled, chronic human immunodeficiency virus type 1 (HIV-1) infection is the absence of strong HIV-1-specific, CD4(+) T-cell-proliferative responses, yet the mechanism underlying this T helper (Th)-cell defect remains controversial. To better understand the impact of HIV-1 replication on Th-cell function, we compared the frequency of CD4(+) Th-cell responses based on production of gamma interferon to lymphoproliferative responses directed against HIV-1 proteins in HIV-1-infected subjects with active in vivo viral replication versus those on suppressed highly active antiretroviral therapy (HAART). No statistically significant differences in the frequencies of cytokine-secreting, HIV-1-specific CD4(+) T cells between the donor groups were found, despite differences in viral load and treatment status. However, HIV-1-specific lymphoproliferative responses were significantly greater in the subjects with HAART suppression than in subjects with active viral replication. Similar levels of HIV-1 RNA were measured in T-cell cultures stimulated with HIV-1 antigens regardless of donor in vivo viral loads, but only HIV-1-specific CD4(+) T cells from subjects with HAART suppression proliferated in vitro, suggesting that HIV-1 replication in vitro does not preclude HIV-1-specific lymphoproliferation. This study demonstrates a discordance between the frequency and proliferative capacity of HIV-1-specific CD4(+) T cells in subjects with ongoing in vivo viral replication and suggests that in vivo HIV-1 replication contributes to the observed defect in HIV-1-specific CD4(+) T-cell proliferation.

Detailed analysis of CD4+ Th responses to envelope and Gag proteins of simian immunodeficiency virus reveals an exclusion of broadly reactive Th epitopes from the glycosylated regions of envelope

Ag-specific CD4(+) Th cells play a key role in the development, maturation, and maintenance of pathogen-specific humoral and cellular immune responses. To define the fine specificity of broadly reactive Th responses associated with mature immunity in a lentiviral system, we analyzed peptide-specific Th responses in eight macaques chronically infected with a reference live attenuated SIV at 12-14 mo postinoculation. All macaques had stable immunocompetent Th cells at the time of analysis, and a unique array of Th responses to 20-mer overlapping peptides from envelope (Env) and Gag was identified for each macaque, which were then used to define a set of 31 broadly reactive peptide epitopes. Only 5 of the 31 broadly reactive Th epitope peptides mapped to the surface (SU) domain of Env. Interestingly, these were all confined to two conserved nonglycosylated regions toward the carboxyl terminus of SU, suggesting a structural influence of glycosylation on development of Th responses. Gag and the Env transmembrane proteins contained the majority of broadly reactive peptide epitopes (12 and 14 peptides, respectively), which were uniformly distributed throughout their sequence. This study defines for the first time broadly reactive Th epitope peptides of SIV Env and Gag proteins that are associated with enduring broadly protective vaccine immunity to attenuated SIV, which may be used for the design and evaluation of experimental vaccines. Moreover, the data suggest that extensive glycosylation of SU may provide yet another immune escape mechanism developed by lentiviruses to restrict the breadth of Th repertoire to SU, a major immunologically exposed protein of the virus.

Immune reconstitution in HIV-1-infected individuals treated with potent antiretroviral therapy

Potent combination antiretroviral therapy that was introduced in the mid-1990s for treatment of HIV-1 infection has resulted in unprecedented decreases in HIV-1 replication and increases in CD4+ T cell counts in many individuals. Coincident with the introduction of potent combination antiretroviral therapy, substantial declines in AIDS-related morbidity and mortality have been observed. Although these declines strongly suggest that significant immune reconstitution is occurring, increasing evidence suggests that immune reconstitution is neither uniform nor complete in all treated individuals. Clinical data suggest that some HIV-1-associated malignancies have not declined despite the new therapies, and that not all treated individuals reconstitute CD4+ T cell numbers to normal values. Laboratory studies reveal that immune responses to ubiquitous antigens are reconstituted, but that responses to rarely encountered antigens, such as tetanus, are not reconstituted without repeat vaccination. Many questions remain concerning the extent and clinical significance of the immune reconstitution that occurs in the setting of antiretroviral drug therapy. A better understanding of the nature of the immune reconstitution that results from potent antiretroviral therapy is critical to the optimal clinical management of HIV-1-infected individuals, and may provide important insights into the immunopathogenesis of HIV-1 infection as well.

Characterization of HIV-specific proliferative T cell responses in HIV-infected persons

Virus-specific helper T cell responses are thought to be an important host defense in HIV infection. The proliferative responses to HIV p24, p55, and gp120 were tested in a cohort of 27 HIV-infected subjects. Vigorous proliferative responses directed at the Gag protein with stimulation indices in excess of 6 were detected in 10 of the individuals tested but an Env-specific response was present in only 1 subject. Viral load and proliferative activity to Gag were inversely correlated in untreated individuals. Proliferation was also observed in some individuals treated in the chronic phase of infection, and responses were maintained over time in the absence of detectable viremia. Positive proliferative responses could also occasionally be detected in treated persons with CD4(+) cell counts below 200/microl. Thus, vigorous Gag-specific proliferative responses are present in a minority of HIV-infected individuals and can be detected in individuals receiving highly active antiretroviral therapy at advanced disease stages. Proliferative responses are maintained for an extended time period in the presence of antiviral therapy.

Prolonged dominance of clonally restricted CD4(+) T cells in macaques infected with simian immunodeficiency viruses

The repertoire of functional CD4(+) T lymphocytes in human immunodeficiency virus type 1-infected individuals remains poorly understood. To explore this issue, we have examined the clonality of CD4(+) T cells in simian immunodeficiency virus (SIV)-infected macaques by assessing T-cell receptor complementarity-determining region 3 (CDR3) profiles and sequences. A dominance of CD4(+) T cells expressing particular CDR3 sequences was identified within certain Vbeta-expressing peripheral blood lymphocyte subpopulations in the infected monkeys. Studies were then done to explore whether these dominant CD4(+) T cells represented expanded antigen-specific cell subpopulations or residual cells remaining in the course of virus-induced CD4(+) T-cell depletion. Sequence analysis revealed that these selected CDR3-bearing CD4(+) T-cell clones emerged soon after infection and dominated the CD4(+) T-cell repertoire for up to 14 months. Moreover, inoculation of chronically infected macaques with autologous SIV-infected cell lines to transiently increase plasma viral loads in the monkeys resulted in the dominance of these selected CDR3-bearing CD4(+) T cells. Both the temporal association of the detection of these clonal cell populations with infection and the dominance of these cell populations following superinfection with SIV suggest that these cells may be SIV specific. Finally, the inoculation of staphylococcal enterotoxin B superantigen into SIV-infected macaques uncovered a polyclonal background underlying the few dominant CDR3-bearing CD4(+) T cells, demonstrating that expandable polyclonal CD4(+) T-cell subpopulations persist in these animals. These results support the notions that a chronic AIDS virus infection can induce clonal expansion, in addition to depletion of CD4(+) T cells, and that some of these clones may be SIV specific.

The role of CD4(+) T helper cells in the cytotoxic T lymphocyte response to HIV-1

Virus-specific CD4(+) T cell help and CD8(+) cytotoxic T cell (CTL) responses are critical for the maintenance of effective immunity in chronic viral infections. HIV-1 infection presents a unique situation in which HIV-1-specific T helper cell responses are characteristically impaired and virus-specific CTLs wane over time as disease progresses; a relationship exists between T cell help and CTL responses in HIV-1 infection.

Nosocomial infections in HIV-infected/AIDS patients

Several pathogenetic processes are involved in the progression to AIDS in HIV-infected individuals. These include a gradual, but ultimately profound, depletion in CD4 lymphocytes, defects in B lymphocytes, neutrophil dysfunction and the breakdown of the integument as a consequence of AIDS-related dermatological conditions such as bacterial and fungal dermatoses and Kaposi's sarcoma. Each of these factors has important implications regarding host susceptibility to nosocomial infections. This review deals with some of the difficulties that are encountered in precisely defining the interrelationships between HIV infection/AIDS and nosocomial sepsis, and some of the controversies that surround respiratory, bloodstream (including central venous catheter-related infections) and gastrointestinal infections that may be acquired within healthcare centres. Because of the lack of accurate, detailed information on this subject, parallels will sometimes be drawn from observations made in other immunologically impaired patient groups and from data examining the rates of community-acquired infections in HIV-infected patients compared to controls. Appropriate and rational infection practice to minimize the risk of acquisition of nosocomial infection is highlighted. Finally, some of the common methodological problems commonly encountered in the current literature regarding nosocomial infections in this population group, and future challenges in the study of these infections, are reviewed.

Activated memory CD4(+) T helper cells repopulate the intestine early following antiretroviral therapy of simian immunodeficiency virus-infected rhesus macaques but exhibit a decreased potential to produce interleukin-2

Using the simian immunodeficiency virus (SIV)-infected rhesus macaque model, we performed a longitudinal study to determine the effect of antiretroviral therapy on the phenotype and functional potential of CD4(+) T cells repopulating intestinal mucosa in human immunodeficiency virus infection. Severe depletion of CD4(+) and CD4(+) CD8(+) T cells occurred in the intestinal mucosa during primary SIV infection. The majority of these cells were of activated memory phenotype. Phosphonate 9-[2-(phosphomethoxypropyl]adenine (PMPA) treatment led to a moderate suppression of intestinal viral loads and repopulation of intestinal mucosa by predominantly activated memory CD4(+) T-helper cells. This repopulation was independent of the level of viral suppression. Compared to preinfection values, the frequency of naive CD4(+) T cells increased following PMPA therapy, suggesting that new CD4(+) T cells were repopulating the intestinal mucosa. Repopulation by CD4(+) CD8(+) T cells was not observed in either jejunum or colon lamina propria. The majority of CD4(+) T cells repopulating the intestinal mucosa following PMPA therapy were CD29(hi) and CD11ahi. A subset of repopulating intestinal CD4(+) T cells expressed Ki-67 antigen, indicating that local proliferation may play a role in the repopulation process. Although the majority of repopulating CD4(+) T cells in the intestinal mucosa were functionally capable of providing B- and T-cell help, as evidenced by their expression of CD28, these CD4(+) T cells were found to have a reduced capacity to produce interleukin-2 (IL-2) compared to the potential of CD4(+) T cells prior to SIV infection. Persistent viral infection may play a role in suppressing the potential of repopulating CD4(+) T cells to produce IL-2. Hence, successful antiretroviral therapy should aim at complete suppression of viral loads in mucosal lymphoid tissues, such as intestinal mucosa.

Lymphoproliferative response to HIV type 1 p24 in long-term survivors of HIV type 1 infection is predictive of persistent AIDS-free infection

To establish immunologic correlates of progression to AIDS in long-term survivors of HIV-1 infection, HIV-1-specific T cell-mediated responses, together with T cell reactivity to recall antigens, were studied in frozen samples collected after 5 and 8 years of documented HIV-1 infection. Eight of 21 homosexual men, who remained asymptomatic and maintained CD4+ T cell numbers >400 cells/microl for 9 years of HIV-1 infection, progressed to AIDS (CDC 1993 definition) within 12.5 years of infection (late progressors, LPs). The remainders showed minimal deterioration of immune parameters (long-term nonprogressors, LTNPs). CD4+ T cell numbers and T cell function measured at years 5 and 8 of follow-up were comparable in the two groups. At both time points responses to recall antigens did not significantly differ between the two groups, although a significant decline of lymphoproliferative responses to Candida and tetanus toxoid was observed in LPs. Circulating HIV-1-specific cytotoxic T lymphocyte precursors were found in broad frequency ranges in both LPs and LTNPs and, similarly, no significant differences were found in comparing the breadth of serum neutralizing activity against heterologous HIV-1 primary isolates. In contrast, lymphoproliferative responses to p24gag, but not p17gag or gp160env, were detected only in LTNPs and were totally absent in LPs at both time points (p < 0.01). Our data suggest that the presence of circulating p24-specific CD4+ T cells may reflect effective viral control and be predictive of subsequent favorable clinical course in long-term asymptomatic individuals.

Simian immunodeficiency virus disease course is predicted by the extent of virus replication during primary infection

To elucidate the relationship between early viral infection events and immunodeficiency virus disease progression, quantitative-competitive and branched-DNA methods of simian immunodeficiency virus (SIV) RNA quantitation were cross-validated and used to measure viremia following infection of rhesus macaques with the pathogenic SIVmac251 virus isolate. Excellent correlation between the methods suggests that both accurately approximate SIV copy number. Plasma viremia was evident 4 days postinfection, and rapid viral expansion led to peak viremia levels of 10(7) to 10(9) SIV RNA copies/ml by days 8 to 17. Limited resolution of primary viremia was accompanied by relatively short, though variable, times to the development of AIDS (81 to 630 days). The persistent high-level viremia observed following intravenous inoculation of SIVmac251 explains the aggressive disease course in this model. Survival analyses demonstrated that the disease course is established 8 to 17 days postinfection, when peak viremia is observed. The most significant predictor of disease progression was the extent of viral decline following peak viremia; larger decrements in viremia were associated with both lower steady-state viremia (P = 0.0005) and a reduced hazard of AIDS (P = 0.004). The data also unexpectedly suggested that following SIVmac251 infection, animals with the highest peak viremia were better able to control virus replication rather than more rapidly developing disease. Analysis of early viral replication dynamics should help define host responses that protect from disease progression and should provide quantitative measures to assess the extent to which protective responses may be induced by prophylactic vaccination.

Effect of protease therapy on cytokine secretion by peripheral blood mononuclear cells (PBMC) from HIV-infected subjects

The viral load reduction seen in patients with late stage HIV infection treated with the protease inhibitor, ritonavir, is accompanied by increases in the in vitro proliferative responses generated by PBMC. The present study was undertaken to investigate which lymphocyte subsets generated these responses and the effects of therapy on cytokine production. Lymphoproliferation following phytohaemagglutinin (PHA) stimulation was studied by thymidine incorporation, and production of IL-2, interferon-gamma (IFN-gamma) and IL-4 was assessed by ELISA in 12 patients receiving ritonavir and seven receiving placebo in the context of randomized, blinded clinical trials. CD4+ cell-depleted and CD8+ cell-depleted subsets were obtained from PBMC by immunomagnetic bead depletion. At week 4 of therapy a two-fold or greater increase in proliferative responses was observed in 9/12 subjects receiving therapy, compared with 0/7 receiving placebo. Similarly there was a significant increase in IL-2 and IFN-gamma production of 2.7-fold (P = 0.02) and 1.7-fold (P = 0.03), respectively, in the treatment group compared with those receiving placebo. No change in IL-4 production was observed. Despite these increases, cytokine responses post-therapy were still reduced compared with both healthy controls and asymptomatic HIV-infected subjects. Increases in proliferative response and IL-2 production were greater in the CD8+ cell-depleted population than in the CD4+ cell-depleted population, whereas increases in IFN-gamma production were derived from the CD4+ cell-depleted population.

In vitro p24 antigen-stimulated lymphocyte proliferation and beta-chemokine production in human immunodeficiency virus type 1 (HIV-1)-seropositive subjects after immunization with an inactivated gp120-depleted HIV-1 immunogen (Remune)

We examined the effect of immune stimulation by a human immunodeficiency virus type 1 (HIV-1) immunogen (Remune) compared to a non-HIV vaccine (influenza) on HIV-1-specific immune responses in HIV-1-seropositive subjects. HIV-1 p24 antigen-stimulated lymphocyte proliferation was not augmented after immunization with the influenza vaccine. In contrast, subjects increased their lymphocyte proliferative responses to p24 antigen after one immunization with HIV-1 immunogen (Remune) (gp120-depleted inactivated HIV-1 in incomplete Freund's adjuvant). Furthermore, p24 antigen-stimulated beta-chemokine production (RANTES, MIP-1alpha, MIP-1beta) was also augmented after immunization with the HIV-1 immunogen but not influenza vaccine. Taken together, these results suggest that in this cohort, HIV-specific immune responses to p24 antigen can be augmented after immunization with an HIV-1 immunogen. The ability to upregulate immune responses to the more conserved core proteins may have important implications in the development of immunotherapeutic interventions for HIV-1 infection.

Intracellular cytokine expression in the CD4+ and CD8+ T cells from intestinal mucosa of simian immunodeficiency virus infected macaques

Isolated intraepithelial lymphocytes (IEL) and lamina propria lymphocytes (LPL) from jejunum of SIV infected animals were examined for alterations in basal cytokine expression by RT-PCR. Remarkable changes in IFNgamma and IL-10 RNA levels were observed in IEL and LPL in SIV infection while IL-4 and IL-2 RNA levels remained unaltered. In addition, the CD4+ and CD8+ LPL were examined for intracellular cytokine production following mitogenic activation by flowcytometry. Both CD4+ and CD8+ T lymphocytes in intestinal mucosa retained the potential to produce IFNgamma in response to mitogenic stimulation in vitro, without a remarkable change in IL-4 production. The dominant IFNgamma cytokine response could be one of the major contributing factors in SIV associated enteropathy.

Safety and immunogenicity of a candidate therapeutic vaccine, p24 virus-like particle, combined with zidovudine, in asymptomatic subjects. Community HIV Research Network Investigators

OBJECTIVES

To evaluate the impact of therapeutic immunization with p24 virus-like particle (VLP) and zidovudine (ZDV) on p24 antibody titre (primary endpoint), CD4+ cell counts, cellular responses to the immunogen and recall antigens, and viral load (secondary endpoints) in subjects with asymptomatic HIV infection and CD4+ counts greater than 400 x 10(6) cells/l.

DESIGN

A double dummy, double-blind randomized placebo-controlled Phase II trial of the therapeutic vaccine p24-VLP, with or without ZDV.

METHODS

ZDV-naive subjects were randomized to one of three groups for 6 months: group A, ZDV 200 mg three times daily plus intramuscular administration of alum adjuvant monthly; group B, ZDV 200 mg three times daily plus p24-VLP (500 microg) in intramuscular alum monthly; group C, placebo capsules plus p24-VLP (500 microg) in intramuscular alum monthly. Subjects were followed for a further 6 months.

RESULTS

Sixty-one patients received vaccinations. The mean CD4+ cell counts pretherapy for groups A, B, and C were 605 +/- 25, 668 +/- 43, and 583 +/- 30 x 10(6) cells/l, respectively. Treatment was well tolerated. At both 24 and 52 weeks there were no significant differences between the treatment groups in terms of antibody responses to p24, CD4+ or CD8+ cell counts, viral load, T-cell responses to p24, p17, recall antigen or mitogen, or markers of immune activation, despite induction of antibody and proliferative responses to the carrier protein of the vaccine.

CONCLUSION

Vaccination with p24-VLP was well tolerated. p24-VLP either alone or in combination with ZDV did not significantly alter either antibody or proliferative responses to p24, or CD4+ cell number, immune activation or viral load over 12 months.

Vigorous HIV-1-specific CD4+ T cell responses associated with control of viremia

Virus-specific CD4+ T helper lymphocytes are critical to the maintenance of effective immunity in a number of chronic viral infections, but are characteristically undetectable in chronic human immunodeficiency virus-type 1 (HIV-1) infection. In individuals who control viremia in the absence of antiviral therapy, polyclonal, persistent, and vigorous HIV-1-specific CD4+ T cell proliferative responses were present, resulting in the elaboration of interferon-gamma and antiviral beta chemokines. In persons with chronic infection, HIV-1-specific proliferative responses to p24 were inversely related to viral load. Strong HIV-1-specific proliferative responses were also detected following treatment of acutely infected persons with potent antiviral therapy. The HIV-1-specific helper cells are likely to be important in immunotherapeutic interventions and vaccine development.

Lymphoproliferative immune function in the Sydney Blood Bank Cohort, infected with natural nef/long terminal repeat mutants, and in other long-term survivors of transfusion-acquired HIV-1 infection

OBJECTIVES

To assess T-helper cell immune function (proliferation) in members of the Sydney Blood Bank Cohort (SBBC) compared with other individuals with transfusion- and sexually acquired HIV-1 infection and with matched HIV-negative controls.

DESIGN AND METHODS

Decreasing CD4 counts and T-helper cell function are associated with disease progression. Peripheral blood mononuclear cells (PBMC) from study subjects were assayed for in vitro proliferative responses to HIV-1-derived antigens, recall antigens and alloantigen. T-helper cell function and CD4 counts in members of the SBBC were followed longitudinally.

RESULTS

Proliferative responses and CD4 counts from members of the SBBC were similar to or better than those of other transfusion- or sexually-acquired HIV-1-positive long-term non-progressors (LTNP), including the HIV-negative matched SBBC control groups. However, individuals with disease progression had reduced or undetectable proliferative responses to recall antigens but a conserved response to alloantigen; they also had low CD4 counts and low CD4:CD8 ratios. In the SBBC, these immune parameters were usually stable over time.

CONCLUSIONS

The unique SBBC with natural nef/long terminal repeat deletions in the HIV-1 genome were genuine LTNP without showing signs of disease progression. They appeared to be a group distinct from the tail-end of the normal distribution of disease progression rates, and may remain asymptomatic indefinitely. The SBBC virus may form the basis of a live attenuated immunotherapeutic or immunoprophylactic HIV vaccine.

Immune reconstitution in HIV infection

Progressive immune deficiency arising during HIV disease reflects the continual degradation and the ultimate deletion of immune specificites defined by the CD4(+) T lymphocyte repertoire. Recent evidence suggests that improvements in the immune function of patients with HIV who receive therapy primarily reflects the expansion of CD4(+) T lymphocyte populations present before therapy commenced. These observations have implications for clinical management, therapeutic strategies, and future research.

HIV-1-Specific Functional Immune Measurements as Markers of Disease Progression

The impairment of lymphocytes to proliferate to HIV antigen is a relatively early functional defect of cell-mediated immunity found in HIV-infected individuals. The finding of strong proliferative responses in nonprogressive HIV disease as well as its inverse association with viral load and clinical manifestation of AIDS supports the further use of this marker as a surrogate of disease progression. The observation that HIV-specific lymphocyte proliferation is associated with the production of CD8-derived HIV suppressive factors such as the beta-chemokines further supports this conclusion. These functional immune measurements provide an additional marker to monitor disease progression in HIV-infected individuals, along with the current standards of CD4 counts and viral load. Copyright 1997 S. Karger AG, Basel

Gag-specific immune responses after immunization with p17/p24:Ty virus-like particles in HIV type 1-seropositive individuals

Gag-specific immune responses and changes in HIV-1 RNA levels were evaluated in eight HIV-1-infected persons, in order to assess the immunotherapeutic potential HIV-1 p17/p24: Ty virus-like particles (p24-VLP). All treated subjects showed transient and dose-dependent proliferative responses to the Ty-VLP carrier (stimulation index [SI], 2.0-119.5). Three of four individuals who received either 500 or 1,000 micrograms of p24-VLP also showed proliferative responses to p17 or p24 (SI, 2.0-15.7). In 2 subjects who were treated with either 500 or 1,000 micrograms of p24-VLP, enhanced Gag-specific CTL precursor (CTLp) frequencies were observed after immunization (10- to 14-fold). Both subjects had low baseline Gag-specific CTL activity (< 25 cTLp/10(6) PBMCs). In the other participants studied no significant boosting of preexisting Gag-specific CTL responses was observed. Short-term elevation of HIV-1 RNA levels at weeks 2 and 4 was observed in two subjects treated with the highest dose of p24-VLP. However, HIV-1 RNA levels at week 24 did not significantly differ from those found in the placebo group. In conclusion, p24-VLP induced marginal Gag-specific immune responses in limited numbers of HIV-1-seropositive individuals, with some showing transient elevation of HIV-1 viral load. Further studies are needed to establish potential clinical effects of these observations.

Expression of CD69 after in vitro stimulation: a rapid method for quantitating impaired lymphocyte responses in HIV-infected individuals

A flow cytometric assay based on expression of the activation antigen CD69 was developed to analyze immunological responses of T cells from human immunodeficiency virus (HIV)-infected (HIV+) or HIV-seronegative (HIV-) donors after in vitro simulation by antigens and polyclonal activators. The levels of CD69 on freshly-isolated or unstimulated, cultured CD3+, CD4+, or CD8+ peripheral blood lymphocyte (PBL) subsets were low and did not differ greatly between HIV+ and HIV- donors. The frequencies of CD3+, CD4+, and CD8+ lymphocytes from HIV+ donors that expressed CD69 after culture with antigenic or mitogenic stimuli were significantly lower than in HIV- donors. Comparison of CD69 expression with [3H]thymidine incorporation revealed that both assays could detect lymphocyte responses to antigenic or mitogenic stimuli. The CD3+ PBL from HIV+ or HIV- donors did not show increased CD69 expression after culture with soluble or cross-linked recombinant envelope glycoprotein, gp120. The gp120, however, significantly inhibited CD69 expression in phytohemagglutinin-stimulated T cells in vitro and may also affect T-cell activation in vivo. These studies demonstrate the usefulness of this CD69 expression assay for the rapid assessment of defects in immune responses of phenotypically defined lymphocyte subsets in HIV+ patients and for testing the effects of agents that modulate immune activation.

In vitro anti-HIV-1 antibody production in subjects in different stages of HIV-1 infection

We evaluated the in vitro antibody production from peripheral blood mononuclear cells (PBMC) against HIV-1 proteins in infected adults. Fifty-four HIV-1 infected patients (four recent seroconverters, 15 asymptomatics with a CD4 count higher than 500/microliters, 27 asymptomatics with a CD4 count between 200 and 500/microliters and eight symptomatic patients) were tested. PBMC were incubated in the presence or absence of 1% pokeweed mitogen (PWM) at 37 degrees C for 8 days. Western blot assay, p24 antigen ELISA and anti-p24 antibody ELISA were performed on serum and culture supernatants. Spontaneous production of anti-env antibody in culture supernatants was evidenced in all subjects. All the positive supernatants for anti-core antibodies (18/54) were derived from asymptomatic patients. PBMC from recent seroconverters and from symptomatic patients did not produce any anti-core antibody. Antibody production decreased after stimulation with PWM. The concentration of p24 antigen did not significantly increase in p24 positive supernatants following acidification (P = 0.1), suggesting that the inability to detect p24 antibody was not due to the anti-p24 antibody complexed to p24 antigen in culture supernatants. In vitro production of anti-p24 antibodies was significantly more frequent in asymptomatic subjects with high CD4+ cell counts (P = 0.02) and was absent in recent seroconverters. This last finding suggests that during the initial phases of the infection, anti-p24 antibody production may be restricted to cells residing in lymphoid organs. In addition, the lower percentage of anti-core antibody in people with low CD4+ cell counts is not merely a consequence of the binding of the antibody to an increased amount of antigen, but probably reflects an impaired production or a sequestration of producing cells in lymphoid tissue during the late stages of the infection.

HIV-specific lymphoproliferative responses in asymptomatic HIV-infected individuals

In vitro lymphoproliferative responses to HIV-1 recombinant antigens (gp160, p24, and Rev protein) were studied in 83 patients with asymptomatic HIV-1 infection (CDC groups II and III) and circulating CD4 lymphocyte numbers > 400/mm3. Significant response to at least one of the three antigens was detected in 52.4% of the subjects, but the responses were weak, and concordance of the response to the three antigens was rare, the frequency of individuals responding to each antigen not exceeding 22.4%. Increasing frequencies of response were observed when recall antigens (tetanus toxoid and Candida albicans glycomannoprotein) (65.5%) and anti-CD3 MoAb (76.6%) were used as stimuli. Although a significant association between lymphocyte response to p24, but not gp160, and steadiness of CD4 lymphocyte numbers before the assay was observed, no predictive value for lack of CD4 cell decrease was confirmed for either antigen, and fluctuation of the responses to HIV antigens was seen during subsequent follow up. The panel of T cell assays used could be regarded as appropriate for monitoring both HIV-specific responses and T lymphocyte function during immunotherapy with soluble HIV antigens.

HIV antigen-reactive T cells detected by antigen-induced interferon gamma secretion

The T cell repertoire to human immunodeficiency virus (HIV) was studied in HIV-infected patients of different clinical stages by the detection and enumeration of cells that secreted interferon gamma (IFN-gamma) in short-term cultures of blood mononuclear cells after stimulation in vitro with the HIV recombinant antigens pB1, p121, p24-15, gp160bac, and the HIV V3 loop peptide. T cell reactivities to cytomegalovirus (CMV) and Mycobacterium tuberculosis-purified protein derivative (PPD) were examined in parallel. Among 29 patients with HIV infection, 48% had blood cells recognizing one or more of the five HIV antigens. The mean numbers of HIV antigen-reactive T cells varied between 1/approximately 6000 blood cells for pB1 and 1/approximately 20,000 cells for p24-15. None of the five HIV antigens studied was identified as an immunodominant T cell epitope in HIV infection. T cells from 20% of the patients responded to all five HIV antigens in parallel, but the antigen preferentially recognized varied from patient to patient. Those with more advanced disease had a tendency to lower numbers of HIV antigen-reactive T cells. Most HIV-infected patients had both CMV- and PPD-reactive T cells, but numbers were significantly lower in more advanced disease. It should be possible to adopt the present method to evaluate fine specificities of the T cell repertoire to other antigens and to study the involvement of other cytokines besides IFN-gamma, for example, the Th2 cell-related cytokine interleukin 4.

Chemoprevention of retroviral infection: success is determined by virus inoculum strength and cellular immunity

We demonstrated earlier that post-exposure prophylaxis with 3'-azido-3'-deoxythymidine (AZT, zidovudine) or with AZT + interferon-alpha (IFN-alpha) prevented viremia and disease in BALB/c mice inoculated with Rauscher murine leukemia virus (RLV). After the 20-day treatment course, most animals were resistant to rechallenge with live virus. Adoptive transfer of T cells from such resistant but not from normal mice into naive recipients provided full protection against virus challenge. From these experiments, we concluded that post-exposure chemoprophylaxis restricted virus replication and allowed the animals to form protective, long-lasting cellular immune responses. Here, the role for cellular immunity during antiviral chemoprophylaxis was tested by comparing treatment success in normal BALB/c mice and in their nude, athymic counterparts. Both were inoculated with equal doses of RLV (10(4) plaque-forming units, pfu). Single-agent AZT or combination therapy with AZT + IFN-alpha, started before or after RLV inoculation, prevented viremia in all normal but not in most nude mice. A significant number of nude mice were completely protected by chemoprevention only when given a 10 times lower virus dose. When normal mice were injected with a 10 times higher virus dose (10(5) pfu), complete protection by chemoprevention was lost. These results demonstrate that the success of chemoprevention depends critically on the virus inoculum. The differential success of chemoprevention in normal and T-cell-deficient mice implies that effective cellular immunity plays an important role in protecting virus-exposed animals against viremia and disease.

B cell activation and human immunodeficiency virus infection. V. Phenotypic and functional alterations in CD5+ and CD5- B cell subsets

B cell dysregulation is a hallmark of human immunodeficiency virus infection. Since B lymphocytes comprise two distinct subpopulations, CD5+ and CD5- cells, we addressed their individual phenotypic and functional behavior. Seropositive patients with both limited and advanced disease progression had an increased percentage of peripheral blood CD5+ B cells, compared to seronegative controls (20.1 +/- 2.1 and 22.7 +/- 5.7, respectively, vs 17.0 +/- 3.4 in controls); however, due to the lymphopenia and reduced number of circulating B cells in infected individuals, the absolute number of CD19+CD5+ lymphocytes was actually reduced. Although HIV-specific antibodies were synthesized spontaneously in vitro only by CD5- B cells, a 10-fold lower degree of spontaneous, non-HIV-specific activation was also displayed by unstimulated CD5+ B cells. These findings indicate that B cell dysregulation during HIV infection involves both the CD5- and the CD5+ B cell compartments; moreover, in view of the putative role of CD5+ B cells in autoimmune phenomena and IL-10 production, these data reinforce the possibility that B cell dysfunction might be causally involved in AIDS pathogenesis.

TGF beta and HIV infection

TGF beta is a cytokine which is involved with the regulation of different aspects of host defense responses to injury. Overexpression of TGF beta can lead to the conversion of its protective functions to pathogenetic manifestations. TGF beta is a potent factor in promoting anabolic aspects in connective tissue metabolism, and uncontrolled production of TGF beta has been associated with the development of fibrosis. With respect to its effects on immune and inflammatory responses, TGF beta is an important endogenous immunosuppressive factor which physiologically may protect the organism from tissue damage caused by chronic activation of leukocytes. As a result of overproduction in HIV infection, this function of TGF beta can contribute to noncytopathic mechanisms of immunodeficiency. TGF beta is involved with several aspects of HIV disease and promotes virus replication and spreading through multiple distinct mechanisms. It directly stimulates virus replication in infected monocytes and peripheral blood mononuclear cells under certain in vitro conditions. It may stimulate the production of other cytokines that enhance virus replication and it may be the mediator of other HIV-stimulating agents such as cocaine. It enhances recruitment of mononuclear phagocytes as cells susceptible to virus infection. Through its profound and broad inhibitory effects on different antiviral defense mechanisms, it facilitates more rapid progression of virus infection and increases susceptibility to opportunistic infections and malignancies. Although these findings are largely based on in vitro systems, the demonstration of TGF beta overexpression in HIV-infected patients supports the notion that this cytokine is an important pathogenetic mediator in HIV infection and its associated diseases. Therapeutic strategies to interfere with these functions of TGF beta are the development of TGF beta-neutralizing antibodies and soluble TGF beta-binding proteins and receptors as well as approaches directed at reducing TGF beta gene expression.

Cell-mediated immunity to HIV-1 in Walter Reed stages 1-6 individuals: correlation with virus burden

Cell-mediated immunity (CMI) to human immunodeficiency virus-1 (HIV-1) was assessed in a blinded fashion for a patient group (n = 79) representing Walter Reed (WR) stages 1-6. At the same time, viral load was quantitatively measured by two different methods, specifically, virus isolation and HIV viral DNA copy number as measured by the polymerase chain reaction (PCR). After unblinding it was determined that the ability to generate a lymphoproliferative response to an inactivated gp120-depleted HIV (HIV-ag) and tetanus toxoid diminished with advancing WR staging, with complete anergy to HIV-ag and tetanus at stage 6. As a group, individuals whose peripheral blood mononuclear cells (PBMC) proliferated to HIV-ag were either virus isolation negative or produced low levels of virus as measured by p24 antigen (< 250 pg p24) on day 7. Similarly, HIV DNA copy number in the HIV-ag responders was low (< 200 copies/4 x 10(5) PBMC). In contrast, antigen proliferation to tetanus toxoid did not correlate with virus load. Thus, clinical progression as defined by the WR staging system appears to coincide with a loss of CMI to HIV. More importantly, the low viral load measured in HIV-ag responders suggests a link between viral burden and CMI to HIV which might be exploited in the design of immunotherapies for HIV-infected individuals.

Use of particulate forms of protein antigens to increase the sensitivity of antigen-specific proliferation assays

Different forms of recombinant HIV-1 gp160 and tetanus toxoid were adsorbed onto latex microspheres and this particulate form of the proteins was used to measure antigen-specific proliferation in vaccinated rhesus macaques. Proliferative responses to proteins bound to microspheres were significantly greater and allowed for the detection of antigen-specific responses that were not detected using soluble proteins. The responses were antigen-specific and required prior immunization of the animals. Additionally, the presence and magnitude of the proliferative responses was associated with antibody responses to the same proteins suggesting the results were representative of in vivo responses and that the assay format did not induce in vitro artifacts.

B cell responses to HIV and the development of human monoclonal antibodies

In this review B cell responses in HIV-infected individuals are summarized together with the techniques used to date to produce human monoclonals to HIV and the properties of these antibodies. Profound disturbances in B cell responses are apparent both in vivo and in vitro. While there is evidence in vivo of marked polyclonal B cell activation, primary and secondary antibody responses are impaired. Similarly these cells exhibit spontaneous immunoglobulin secretion upon in vitro culture but do not readily respond to B cell mitogens and recall antigens including HIV. Furthermore, certain of these defects can be reproduced in normal B cells in vitro by incubation with HIV or HIV coded peptides. Individuals infected with HIV develop antibodies to HIV structural proteins (e.g. p17, p24, gp41 and gp120) and regulatory proteins (e.g. vif, nef, RT). Autoantibodies against a number of immunologically important molecules are also frequently observed. The anti-HIV antibodies are predominantly of the IgG1 isotype and exhibit a variety of effects on the virus in vitro. To date, using conventional immortalization strategies, an appreciable number of human monoclonals to HIV have been developed. These have been specific for gp41, gp120 and gag with antibodies of the former specificity predominating. The majority of these antibodies have been of the IgG1 isotype. Only a small number of the antibodies neutralize virus in vitro and most of these react with gp120. The neutralizing antibodies recognize conformational and carbohydrate epitopes or epitopes in amino acid positions 306-322. The predominant epitopes recognized by the anti-gp41 antibodies were in amino acid positions 579-620 and 644-662. A high percentage (congruent to 25%) of these antibodies enhance viral growth in vitro. The problems relating to the production of human monoclonals to HIV are discussed together with strategies that could be used in the future.

Immunological changes in cats with concurrent Toxoplasma gondii and feline immunodeficiency virus infections

To examine the immunological changes in cats concurrently infected with feline immunodeficiency virus (FIV) and Toxoplasma gondii, kittens (four per group) were inoculated with FIV, T. gondii, both agents, or no pathogens. Blood mononuclear cells and plasma were collected weekly for lymphocyte assays and serology. At week 14, spleen and lymph node cells were used for lymphocyte assays; brains and mesenteric lymph nodes were used for isolation of T. gondii. More T. gondii organisms were present in tissues of the dually infected cats than in tissues of cats with toxoplasmosis alone. Two dually infected cats and one cat infected with T. gondii developed chorioretinitis. Spleen, lymph node, and blood mononuclear cells from dually infected cats had the greatest reduction in mitogenic responses. By week 3, cats infected with FIV underwent a decrease in the number of CD4 cells that was not changed by concurrent T. gondii infection; the number of CD8 cells increased only in cats infected with T. gondii alone. For cats infected with T. gondii, the responses of lymphocytes to T. gondii antigen were not affected by FIV infection; the responses to FIV antigen were negligible in all groups. Overall, this study indicates that FIV infection favors T. gondii proliferation. Also, the establishment of toxoplasmosis may enhance FIV-induced immunodeficiency and is likely to cause a more rapid disease progression than that from infection with FIV alone.

Cellular and antibody responses directed against the HIV-1 principal neutralizing domain in HIV-1-infected children

The principal neutralizing domain (PND) for antibody response is located within the V3 variable region of gp120 and can also stimulate T-cell responses. In some adults infected with human immunodeficiency virus (HIV) an HIV-1-specific T-cell response can be detected by demonstrating in vitro proliferation to HIV-1 proteins and peptides. In other HIV-1 infected adults an HIV-1-specific T-cell response can involve interleukin 2 (IL-2) secretion in the absence of T-cell proliferation. To elucidate the T-cell responses to PND in children, we examined the proliferative and the IL-2 secretory responses of peripheral blood lymphocytes from 19 HIV-1-infected children toward a peptide which contained a highly conserved sequence of the principal neutralizing domain of HIVMN (PND-MN). Stimulation with PND-MN induced proliferation of lymphocytes from 2 of the children and IL-2 secretion by lymphocytes from 5 of the children. In a 3-month-old infant, the in vitro cellular response to the PND-MN indicated HIV-1 infection prior to the detection p24 antigen in her serum. Although antibodies directed against PND-MN were detected in all but one of the children examined, the presence of high-affinity/avidity antibodies to the PND-MN correlated with the presence of a cellular response to PND-MN. Thus, in HIV-1-infected children an HIV-1 specific T-cell response in the absence of a proliferative response can be assessed by determination of the IL-2 secretory response and correlates with the generation of high-affinity/avidity antibodies.

Epitopes of human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins recognized by antibodies in the sera of HIV-1-infected individuals

Sera from human immunodeficiency virus (HIV)-infected study subjects and controls were analyzed by enzyme-linked immunosorbent assay using 10 synthetic peptides to identify epitopes of HIV envelope glycoproteins (ENVgp) that were recognized by antibodies. Two epitopes of HIV ENVgp, ENVP466 (amino acids 466-481) and ENVP497 (amino acids 497-509), were recognized by antibodies in the sera of most HIV-infected individuals. The frequency of individuals with detectable serum antibodies to these two epitopes was not associated with the stage of HIV disease. Purified antibodies to ENV497 had only very weak neutralizing activity against infectious HIV. These data suggest that a particular dominant type of antibody response to HIV's ENVgp has minimal protective effects. These and other studies to identify and stimulate immune responses to selected epitopes of HIV antigens may be useful in the design of vaccines to prevent or treat HIV infections.