The decay of the latent reservoir of replication-competent HIV-1 is inversely correlated with the extent of residual viral replication during prolonged anti-retroviral therapy

Replication-competent HIV-1 can be isolated from infected patients despite prolonged plasma virus suppression by anti-retroviral treatment. Recent studies have identified resting, memory CD4+ T lymphocytes as a long-lived latent reservoir of HIV-1 (refs. 4,5). Cross-sectional analyses indicate that the reservoir is rather small, between 103 and 107 cells per patient. In individuals whose plasma viremia levels are well suppressed by anti-retroviral therapy, peripheral blood mononuclear cells containing replication-competent HIV-1 were found to decay with a mean half-life of approximately 6 months, close to the decay characteristics of memory lymphocytes in humans and monkeys. In contrast, little decay was found in a less-selective patient population. We undertook this study to address this apparent discrepancy. Using a quantitative micro-culture assay, we demonstrate here that the latent reservoir decays with a mean half-life of 6.3 months in patients who consistently maintain plasma HIV-1 RNA levels of fewer than 50 copies/ml. Slower decay rates occur in individuals who experience intermittent episodes of plasma viremia. Our findings indicate that the persistence of the latent reservoir of HIV-1 despite prolonged treatment is due not only to its slow intrinsic decay characteristics but also to the inability of current drug regimens to completely block HIV-1 replication.

HIV-1 drug resistance in newly infected individuals

CONTEXT

There is concern that the widespread use of antiretroviral drugs to treat human immunodeficiency virus 1 (HIV-1) infection may result in the increased transmission of drug-resistant virus.

OBJECTIVE

To determine the prevalence of drug resistance-conferring mutations and phenotypic resistance to antiretroviral agents in a cohort of individuals newly infected with HIV-1.

DESIGN

Case series with genetic analyses of the HIV-1 plasma-derived pol gene using reverse transcriptase polymerase chain reaction followed by direct sequencing of polymerase chain reaction products. Phenotypic analysis was performed with a recombinant virus assay.

SETTING AND PATIENTS

Eighty individuals referred, on average, 1.7 months after infection with HIV-1 to the Aaron Diamond AIDS Research Center between July 1995 and April 1999. Subjects were from large urban areas (65 from New York, NY; 11 from Los Angeles, Calif); 60 (75%) were white, and 75 (93.8%) were homosexual men.

MAIN OUTCOME MEASURES

Prevalence of known resistance-conferring genotypes and reduced susceptibility to individual antiviral agents by phenotype.

RESULTS

Thirteen individuals (16.3%) had genotypes associated with drug resistance to any antiretroviral agent. Virus with known resistance-conferring mutations to any nucleoside reverse transcriptase inhibitors was found in 10 individuals, to any nonnucleoside reverse transcriptase inhibitors in 6 subjects, and to any protease inhibitors in 2 cases. Multidrug-resistant virus was identified in 3 individuals (3.8%). Extensive polymorphism in the protease gene was identified. Interpretation of genotypes and phenotypes was concordant in 57 (85%) of the 67 cases in which both studies were performed.

CONCLUSION

The prevalence of HIV-1 variants with known resistance-conferring genotypes to any antiretroviral agent in this cohort of 80 newly infected individuals is 16.3%. These data support expanded use of resistance testing in the setting of primary HIV-1 infection. Clinical trials should be initiated to establish whether therapy guided by resistance testing, compared with the use of empirical triple combination antiretroviral therapy, provides additional virological and immunological benefit when treating primary HIV-1 infection. Further efforts to expand the study of transmission of drug-resistant HIV-1 variants, particularly in cohorts with different epidemiological profiles, are indicated.

JC virus DNA load in patients with and without progressive multifocal leukoencephalopathy

OBJECTIVE

To determine the clinical value of JC virus (JCV) detection in various anatomic compartments for the diagnosis of progressive multifocal leukoencephalopathy (PML).

METHODS

CSF, peripheral blood mononuclear cells (PBMC), plasma, and urine samples were evaluated from HIV-infected and uninfected individuals. JCV DNA was detected by PCR and was quantified using a competitive PCR ELISA.

RESULTS

JCV DNA was detected in one-third of the urine samples, regardless of HIV serostatus or clinical evidence of PML. JCV DNA was detected in five of eight PBMC and three of seven plasma samples of HIV-positive PML patients, in 13 of 103 PBMC and 7 of 32 plasma samples of HIV-positive persons without PML, but in 0 of 18 PBMC and 0 of 13 plasma samples of HIV-negative control subjects. There was no correlation between the presence of JCV DNA in the PBMC and plasma, but the detection of JCV in either compartment was associated with low CD4+ lymphocyte counts. JCV DNA was not detected in the CSF of 27 of 27 HIV-negative persons and 64 of 65 HIV-positive persons without PML, but was found in the CSF of three of three HIV-negative immunosuppressed individuals and 10 of 11 HIV-positive individuals with clinical and radiologic evidence of PML, confirmed by biopsy in four of four tested patients. PBMC harbored 10 to 90 JCV copies/microg DNA, and the CSF of the PML patients contained 3.65 x 10(4) to 2.04 x 10(5) JCV copies/mL CSF.

CONCLUSIONS

JCV viruria was found as frequently in HIV-positive individuals as in control subjects, suggesting that its detection has no clinical value. JCV detection in the blood correlates with immunosuppression and not with PML. The presence of JCV in the CSF is highly sensitive and specific for PML, and a high CSF JC viral load was associated with poor clinical outcome in patients receiving antiretroviral therapy. JCV quantification in the CSF constitutes a potentially important tool for monitoring clinical PML treatment trials.

Non-sensitizing epicutaneous skin tests prevent subsequent induction of immune tolerance

Oral administration of nickel or chromium to naive guinea pigs results in immune unresponsiveness to subsequent induction of allergic contact hypersensitivity. Such "oral tolerance" depends on the oral dose, is antigen specific, T-suppressor-cell mediated, and very persistent. In contrast, oral antigen administration to sensitized animals results at best in transient desensitization. Here we report that even non-sensitizing epicutaneous skin contacts prevented the subsequent induction of oral tolerance. These data support the view that primed T cells are less sensitive to suppressor T-cell function than naive T cells.

Oral induction of tolerance to nickel sensitization in mice

Antigen contact via the alimentary tract prior to sensitization may result in systemic immunologic unresponsiveness ("oral tolerance"). The induction of oral tolerance seems an attractive strategy to combat undesired immune responses, such as allograft rejection and autoimmune and allergic diseases. We describe clear and reproducible sensitization to nickel in mice reared under nickel-free conditions. Hypersensitivity was induced by injecting nickel sulfate intradermally into the flank skin and elicited by injecting the metal salt into the pinnae of the ears. The effectiveness of orally induced hyporesponsiveness could be inferred from a low degree of hypersensitivity obtained with mice raised and maintained in cages with nickel-releasing covers and water nipples. This mouse model for the assay of nickel hypersensitivity was used for oral tolerance studies by administrating non-toxic doses of nickel sulfate in drinking water or intragastrically prior to sensitization. In these animals, the development of delayed-type hypersensitivity was suppressed in a dose-dependent way, and the hyporesponsiveness could be transferred by CD8+ cells. The antigen specificity of this oral tolerance could be demonstrated by the concomitant use of sensitization and challenge procedures for nickel and chromium. The hypersensitivity assay described provides a versatile, highly reproducible experimental model to study immunoregulation of oral tolerance to clinically relevant metal allergens.

Persistent immune tolerance to nickel and chromium by oral administration prior to cutaneous sensitization

Oral administration of allergens, foreign proteins, or cell-bound antigens may induce systemic suppression of subsequent humoral and cell-mediated immune responses ("oral tolerance"). The induction of specific immune tolerance provides a potential strategy for treatment of T-cell-dependent immune diseases. Therefore, in depth studies into preconditions for optimal and persistent tolerance induction are mandatory. Here we report on such studies in a guinea pig model using the non-cross-reactive contact allergens nickel and chromium. Feeding per os of nickel sulfate or potassium dichromate did not trigger systemic TDTH-effector functions. Instead, short feeding periods led to a dose-dependent, and metal-specific, suppression of subsequently induced allergic contact hypersensitivity. Administration of the allergens onto the oral mucosa was most effective in the induction of immune tolerance. When first sensitizing attempts were delayed until 1 year after feeding, the degree of unresponsiveness was reduced. In contrast, with cutaneous contacts starting shortly after the feeding period, tolerance was fully stable and undiminished for at least 2 years. Thus, in orally treated guinea pigs cutaneous contacts provide boosting tolerogenic signals, supporting the view that oral tolerance does not result from clonal deletion but from active antigen-specific immunosuppression. Indeed, unresponsiveness to cutaneous immunization could be transferred by lymphoid cells from fed guinea pigs in a metal-specific way.

Development of a concomitant nickel and chromium sensitization model in the guinea pig

Although nickel allergy is the most frequent contact hypersensitivity in man, reports on successful nickel sensitization in experimental animals are scarce. Chromium hypersensitivity, on the other hand, is readily induced in guinea pigs. In this study we set out to obtain reproducible nickel sensitization in guinea pigs, in order to establish an animal model for immunospecific tolerance and desensitization studies in which two non-cross-reacting metal allergens, chromium and nickel, could be studied simultaneously. Strong and reproducible sensitization to nickel was achieved by injecting low amounts of Freund's complete adjuvant and nickel sulfate in a split-adjuvant procedure. Strong erythematous reactions were observed as early as 14 days after sensitization and could be elicited both by intradermal and open epicutaneous challenges. Optimal evaluation was with nickel sulfate administered epicutaneously in 40% dimethyl sulfoxide to enhance skin penetration. Hypersensitivity could be transferred with lymphocytes and not with serum. Sensitization procedures for nickel and chromium then could successfully be combined in a double sensitization procedure. With four different guinea pig strains no genetic restriction was observed for the induction of nickel or chromium sensitivity. However, for both metals a clear sex and age dependence was observed: female guinea pigs reached a higher degree of sensitization than males, whereas sensitization in young animals was relatively weak.

Reduced frequency of nickel allergy upon oral nickel contact at an early age

From animal studies we know that oral administration of T-dependent antigens before sensitization effectively induces systemic immune unresponsiveness. Such 'oral tolerance' is persistent, dose-dependent, antigen-specific and presumably T suppressor cell-mediated. Oral tolerance induction could be an effective way to prevent undesired T cell-mediated immune functions, such as playing a role in allograft reaction, autoimmune and allergic diseases. In the present study allergic contact hypersensitivity (ACH) to nickel, currently presenting the most frequent contact allergy in man, was chosen to establish the feasibility of oral prevention of undesired T cell-mediated immunity in man. Potentially tolerizing (oral nickel contacts via orthodontic braces) as well as sensitizing (ear piercing) events were studied retrospectively in 2176 patients attending nine European patch test clinics. Patients were interviewed by means of a confidential questionnaire. The results show that ear piercing strongly favoured development of nickel ACH. More importantly, patients having had oral contacts with nickel-releasing appliances (dental braces) at an early age, but only if prior to ear piercing, showed a reduced frequency of nickel hypersensitivity. Frequencies of other hypersensitivities, in particular to fragrance, were not affected. These results support our view that induction of specific systemic immunologic tolerance by timely oral administration of antigens is feasible in man.

The influence of the thymus on precursor T cells

The influence of the thymus on its bone marrow precursors was investigated: T cell differentiation was studied in irradiated mice reconstituted with bone marrow from thymectomized donors. Up to twelve months after TX the influx of precursors and differentiation into T cells were not changed in the recipients. CFU-s determination of bone marrow and spleen from thymectomized animals did not show a change in numbers but during ageing a shift of the E/G ratio was observed in thymectomized as well as control donors.

Functional and morphological recovery of the T-cell compartment in lethally irradiated and reconstituted mice

The recovery of the T-cell compartment in mice after lethal irradiation and reconstitution was studied using functional and morphological parameters. T-helper cell activity, determined by the direct SRBC-plaque-forming cell (PFC) response, recovers in a similar fashion as T-memory function which was studied by adoptive transfer of carrier-primed cells. Both functions return to control levels in 2.5-3 months. Using immunoperoxidase staining of frozen sections with anti-T cell serum, the morphological recovery of the T-cell dependent areas in the white pulp of the spleen could be studied and compared with the functional recovery.

The specificity of heterologous antiserum against brain of nude mice

Serum prepared in rabbits against brain of nude mice was tested for its T-cell specificity by immunoperoxidase staining. The difference in activity of this anti-brain serum against early precursors and more differentiated precursors of the haemopoietic cell lines was investigated by CFU-s and CFU-c determination after serum incubation. The results showed that the activity of the anti-nude brain serum is completely comparable to serum prepared against brain of normal mice.

Early kinetics of B cell memory and the influence of T cells on the expression in vitro

To study the early kinetics of B cell memory to sheep erythrocytes mouse spleen cells were cultured after short priming times in vivo. The influence of T cells on the expression of memory in vitro was investigated by treatment with anti-theta serum. Within 48 hours of in vivo priming part of the B cell population can differentiate into cells capable of IgG production after secondary antigen contact in vitro without the help of T cells. The presence of antigen was required for the in vitro development.