Effects of passive immunization in patients with the acquired immunodeficiency syndrome-related complex and acquired immunodeficiency syndrome

Passive Immunisation in the Treatment of Infectious Diseases Related to Highly Potent Bacterial Toxins

The discovery of microbial toxins as the primary factors responsible for disease manifestations and the discovery that these toxins could be neutralised by antitoxins are linked to the birth of immunology. In the late 19th century, the serum or plasma of animals or patients who had recovered from infectious diseases or who had been immunised with a relevant antigen began to be used to treat or prevent infections. Before the advent of widespread vaccination campaigns, antitoxins played a key role in the treatment and prevention of diseases such as diphtheria and tetanus. A significant reduction in mortality following the introduction of antitoxins confirmed their efficacy. Serum therapy remains an important measure for post-exposure prophylaxis and for the treatment of unvaccinated or incompletely vaccinated patients. For the botulinum toxin, antitoxin therapy continues to be the sole available treatment. The manuscript contains a summary of the most important information on the passive immunoprophylaxis used in the treatment of diphtheria, tetanus, and botulism, all representing diseases in which symptoms are driven by the activity of highly potent bacterial toxins.

Broadly neutralizing antibodies for HIV prevention: a comprehensive review and future perspectives

SUMMARYThe human immunodeficiency virus (HIV) epidemic remains a formidable global health concern, with 39 million people living with the virus and 1.3 million new infections reported in 2022. Despite anti-retroviral therapy's effectiveness in pre-exposure prophylaxis, its global adoption is limited. Broadly neutralizing antibodies (bNAbs) offer an alternative strategy for HIV prevention through passive immunization. Historically, passive immunization has been efficacious in the treatment of various diseases ranging from oncology to infectious diseases. Early clinical trials suggest bNAbs are safe, tolerable, and capable of reducing HIV RNA levels. Although challenges such as bNAb resistance have been noted in phase I trials, ongoing research aims to assess the additive or synergistic benefits of combining multiple bNAbs. Researchers are exploring bispecific and trispecific antibodies, and fragment crystallizable region modifications to augment antibody efficacy and half-life. Moreover, the potential of other antibody isotypes like IgG3 and IgA is under investigation. While promising, the application of bNAbs faces economic and logistical barriers. High manufacturing costs, particularly in resource-limited settings, and logistical challenges like cold-chain requirements pose obstacles. Preliminary studies suggest cost-effectiveness, although this is contingent on various factors like efficacy and distribution. Technological advancements and strategic partnerships may mitigate some challenges, but issues like molecular aggregation remain. The World Health Organization has provided preferred product characteristics for bNAbs, focusing on optimizing their efficacy, safety, and accessibility. The integration of bNAbs in HIV prophylaxis necessitates a multi-faceted approach, considering economic, logistical, and scientific variables. This review comprehensively covers the historical context, current advancements, and future avenues of bNAbs in HIV prevention.

Exploring HIV Vaccine Progress in the Pre-Clinical and Clinical Setting: From History to Future Prospects

The human immunodeficiency virus (HIV) continues to pose a significant global health challenge, with millions of people affected and new cases emerging each year. While various treatment and prevention methods exist, including antiretroviral therapy and non-vaccine approaches, developing an effective vaccine remains the most crucial and cost-effective solution to combating the HIV epidemic. Despite significant advancements in HIV research, the HIV vaccine field has faced numerous challenges, and only one clinical trial has demonstrated a modest level of efficacy. This review delves into the history of HIV vaccines and the current efforts in HIV prevention, emphasizing pre-clinical vaccine development using the non-human primate model (NHP) of HIV infection. NHP models offer valuable insights into potential preventive strategies for combating HIV, and they play a vital role in informing and guiding the development of novel vaccine candidates before they can proceed to human clinical trials.

Broadly neutralizing antibodies for HIV treatment and cure approaches

PURPOSE OF REVIEW

In recent years, clinical trials have explored broadly neutralizing antibodies (bNAbs) as treatment and cure of HIV. Here, we summarize the current knowledge, review the latest clinical studies, and reflect on the potential role of bNAbs in future applications in HIV treatment and cure strategies.

RECENT FINDINGS

In most individuals who switch from standard antiretroviral therapy to bNAb treatment, combinations of at least two bNAbs effectively suppress viremia. However, sensitivity of archived proviruses to bNAb neutralization and maintaining adequate bNAb plasma levels are key determinants of the therapeutic effect. Combinations of bNAbs with injectable small-molecule antiretrovirals are being developed as long-acting treatment regimens that may require as little as two annual administrations to maintain virological suppression. Further, interventions that combine bNAbs with immune modulators or therapeutic vaccines are under investigation as HIV curative strategies. Interestingly, administration of bNAbs during the early or viremic stage of infection appears to enhance host immune responses against HIV.

SUMMARY

While accurately predicting archived resistant mutations has been a significant challenge for bNAb-based treatments, combinations of potent bNAbs against nonoverlapping epitopes may help overcome this issue. As a result, multiple long-acting HIV treatment and cure strategies involving bNAbs are now being investigated.

Trends in CD4+ cell counts, viral load, treatment, testing history, and sociodemographic characteristics of newly diagnosed HIV patients in Osaka, Japan, from 2003 to 2017: a descriptive study

BACKGROUND

The CD4 cell count of patients during diagnosis and distribution of CD4 cell counts in the patient population are important to understand infection-diagnosis interval and incidence rate of human immunodeficiency virus (HIV) infection, respectively. However, this information has not been published in Japan. This study aimed to describe the change in CD4 cell count trend and clarify the change in patients' characteristics in association with the CD4 cell count information.

METHODS

A descriptive study was conducted to analyze the medical records of patients with HIV who visited one of the largest acquired immunodeficiency syndrome (AIDS) core hospitals in western Japan. The basic characteristics, CD4 cell counts, viral load, and diagnosis-treatment interval between the first (2003-2010) and second (2011-2017) halves of the study duration were compared.

RESULTS

The distribution of the CD4 cell counts significantly changed between 2003-2010 and 2011-2017 (χ² = 20.42, p < 0.001). The proportion of CD4 cell count <200 cells/mm³ increased (38.8% in 2003 to 45.9% in 2017), whereas CD4 cell count ≥500 cells/mm³ decreased (19.4% in 2003 to 12.2% in 2017). Moreover, the distributions of age groups, history of HIV screening test, patient outcomes, HIV viral load, and diagnosis-treatment interval also significantly changed (χ² = 25.55, p < 0.001; χ² = 8.37, p = 0.015; χ² = 6.07, p = 0.014; χ² = 13.36, p = 0.020; χ² = 173.76, p < 0.001, respectively).

CONCLUSION

This study demonstrated the fundamental trends of the HIV epidemic in Osaka, Japan, and indicated the incidence rate of HIV was decreasing in Japan.

Preventive HIV Vaccines-Leveraging on Lessons from the Past to Pave the Way Forward

Almost four decades on, since the 1980’s, with hundreds of HIV vaccine candidates tested in both non-human primates and humans, and several HIV vaccines trials later, an efficacious HIV vaccine continues to evade us. The enormous worldwide genetic diversity of HIV, combined with HIV’s inherent recombination and high mutation rates, has hampered the development of an effective vaccine. Despite the advent of antiretrovirals as pre-exposure prophylaxis and preventative treatment, which have shown to be effective, HIV infections continue to proliferate, highlighting the great need for a vaccine. Here, we provide a brief history for the HIV vaccine field, with the most recent disappointments and advancements. We also provide an update on current passive immunity trials, testing proof of the concept of the most clinically advanced broadly neutralizing monoclonal antibodies for HIV prevention. Finally, we include mucosal immunity, the importance of vaccine-elicited immune responses and the challenges thereof in the most vulnerable environment–the female genital tract and the rectal surfaces of the gastrointestinal tract for heterosexual and men who have sex with men transmissions, respectively.

Broadly Neutralizing Antibodies for HIV Prevention

In the last decade, over a dozen potent broadly neutralizing antibodies (bnAbs) to several HIV envelope protein epitopes have been identified, and their in vitro neutralization profiles have been defined. Many have demonstrated prevention efficacy in preclinical trials and favorable safety and pharmacokinetic profiles in early human clinical trials. The first human prevention efficacy trials using 10 sequential, every-two-month administrations of a single anti-HIV bnAb are anticipated to conclude in 2020. Combinations of complementary bnAbs and multi-specific bnAbs exhibit improved breadth and potency over most individual antibodies and are entering advanced clinical development. Genetic engineering of the Fc regions has markedly improved bnAb half-life, increased mucosal tissue concentrations of antibodies (especially in the genital tract), and enhanced immunomodulatory and Fc effector functionality, all of which improve antibodies' preventative and therapeutic potential. Human-derived monoclonal antibodies are likely to enter the realm of primary care prevention and therapy for viral infections in the near future.

Broadly Neutralizing Antibodies for HIV Eradication

Passive transfer of antibodies has long been considered a potential treatment modality for infectious diseases, including HIV. Early efforts to use antibodies to suppress HIV replication, however, were largely unsuccessful, as the antibodies that were studied neutralized only a relatively narrow spectrum of viral strains and were not very potent. Recent advances have led to the discovery of a large portfolio of human monoclonal antibodies that are broadly neutralizing across many HIV-1 subtypes and are also substantially more potent. These antibodies target multiple different epitopes on the HIV envelope, thus allowing for the development of antibody combinations. In this review, we discuss the application of broadly neutralizing antibodies (bNAbs) for HIV treatment and HIV eradication strategies. We highlight bNAbs that target key epitopes, such as the CD4 binding site and the V2/V3-glycan-dependent sites, and we discuss several bNAbs that are currently in the clinical development pipeline.

Postconditioning hormesis put in perspective: an overview of experimental and clinical studies

A beneficial effect of applying mild stress to cells or organisms, that were initially exposed to a high dose of stress, has been referred to as 'postconditioning hormesis'. The initial high dose of stress activates intrinsic self-recovery mechanisms. Modulation of these endogenous adaptation strategies by administration of a subsequent low dose of stress can confer effects that are beneficial to the biological system. Owing to its potentially therapeutic applications, postconditioning hormesis is subject to research in various scientific disciplines. This paper presents an overview of the dynamics of postconditioning hormesis and illustrates this phenomenon with a number of examples in experimental and clinical research.

APPLICATION OF VIP/NTM-REACTIVE NATURAL ANTIBODIES IN THERAPY OF HIV DISEASE

In sera of HIV-infected individuals natural antibodies recognizing nonimmunogenic C-terminal domain of the second conserved region of HIV-1 gp120 and the vasoactive intestinal peptide (VIP) were identified. It has been demonstrated that these antibodies are significantly more prevalent in asymptomatic carriers than in AIDS patients and that their titer strongly correlates with disease progression. These findings point out the VIP/C2-reactive natural antibodies as an important agent for immunotherapy of HIV disease.

High level serum neutralizing antibody against HIV-1 in Chinese long-term non-progressors

NAb have been considered to be an important component of a protective immune response to HIV-1, yet the relationship between the capacity of HIV-1 NAb, the conserved neutralization epitopes and disease progression has been unclear. To gain a better understanding of the protective roles that NAb and conserved neutralization epitopes could play in LTNP, twenty-eight HIV-1-infected subjects were investigated by evaluation of the concentrations of HIV-1 NAb and conserved neutralization epitopes, using single-round PBMC neutralization assay and sequencing. Our study revealed that the concentration of NAb in LTNP was significantly higher than that in subjects with asymptomatic HIV (P < 0.05) and AIDS (P < 0.01). No amino acids substitutions were found in the conserved epitopes of the HIV-1 gp120 region in LTNP, whereas the viruses circulating both in persons with asymptomatic HIV and those with AIDS had amino acid substitutions in their conserved neutralization epitopes. This study suggests that high levels of NAb and stable epitopes in gp120 could play a crucial role in protection against disease progression.

Clinical experience with therapeutic AIDS vaccines

Recently, there has been a renewed interest in therapeutic vaccination as an adjunct or alternative to current treatment options for HIV. The first immunotherapeutic trial relevant to this topic was published in 1983. Since then, several dozen therapeutic vaccine trials have been carried out. The results have consistently shown that although in vitro-measured HIV-specific immune responses were evident as a result of vaccination, clinical improvement has been seldom observed. The instances of apparent clinical benefit however, were invariably associated with the usage of vaccines that acted in accord with the principles of allo- or autoimmunization. The majority of these vaccines were derived from the blood of HIV carriers or a cell culture and therefore inherently contained host-cell antigens unrelated to HIV. These observations raise the issue of whether this clinically successful approach has been unduly neglected. Most commercial vaccines on the market today are made the old-fashioned way, but very little support or attention has been given to the development of such vaccines for AIDS therapy. The current strategy, biased toward vaccines which have shown little evidence of clinical efficacy, is shortsighted and needs to be revised.

Human retroviruses in leukaemia and AIDS: reflections on their discovery, biology and epidemiology

The study of retroviruses has had a profound impact by unveiling an unusual form of viral replication: the multiplication of RNA viruses via a proviral DNA, for which Jan Svoboda provided the experimental model over forty years ago. In 1970 Temin, Mizutani and Baltimore discovered that this group of viruses contains a unique enzyme catalysing the synthesis of a DNA copy of the viral RNA: reverse transcriptase (RT). The discovery of RT has itself had an enormous impact on molecular biology in general, but also stimulated many premature claims of its detection in human disease. Claims by Gallo's laboratory that the cytoplasm of human leukaemia cells contained RT proved to be unfounded, as did his report in collaboration with Weiss that myeloid leukaemia contained HL23 virus, this organism proving not to be human but a laboratory contaminant of three monkey viruses. Conclusive demonstration of a retroviral involvement in human leukaemia was first provided in 1981 by Hinuma and his associates, showing that adult T-cell leukaemia (ATL), a rare form of leukaemia endemic to south-west Japan, is caused by a new retrovirus (ATLV). Other publications in December 1980 and through 1981 claimed the discovery of a new human T-cell leukaemia virus involved in mycosis fungoides (MF) and Sézary's syndrome (SS). This virus was termed HTLV by Gallo. The nucleotide sequence of ATLV is strongly conserved, that of my 1983 isolate from a black British ATL patient being practically identical with the Japanese virus isolates. After AIDS was recognised in 1981 by Gottlieb and coworkers as a new human disease, several papers were published by Gallo and his associates during 1983-4, invoking the oncovirus responsible for adult T-cell leukaemia as the cause of AIDS. In 1983 the French scientist Barré-Sinoussi and her colleagues succeeded in isolating a new agent in the disease, a lentivirus, which they named LAV. The French immunologist Klatzmann and his colleagues discovered that LAV killed CD4+ T-cells, furnishing an explanation for the pathogenesis of AIDS and providing a mechanism for how AIDS developed. For some time Gallo continued to suggest leukaemia virus involvement, claiming that his independent isolate of the AIDS virus, termed HTLV-III, was closely related to HTLV-I (the Japanese ATLV). Although this created considerable confusion among researchers for a period, the relationship was eventually disproved. Unlike ATLV, whose nucleic acid sequence is very stable, the AIDS virus (now termed HIV by international agreement) is extraordinarily unstable, the sequences of independent HIV isolates being quite unique: this made it possible to establish conclusively that both HTLV-III and another independent isolate CBL-1, from Weiss' laboratory, were actually LAV isolates from the French laboratory. It has been shown by Hayami and his associates that only African primates are infected with similar lentiviruses to HIV which explains why AIDS started in Africa. Further research has clarified the origin of HIV-1 to be a chimpanzee lentivirus and HIV-2 to be the sooty mangabey lentivirus, which began to spread in humans perhaps no more than fifty years ago. The infection has spread rapidly, primarily through sexual intercourse, but also by transmission through blood and its products as well as contaminated needles and syringes. Sexual intercourse has now spread the virus around the World; and there are probably some 70 million infected. 90% of those infected with HIV develop the deadly disease of AIDS within ten years of infection: the death toll from the disease has been enormous. By contrast, HTLV-1 has been infecting man in isolated areas probably for hundreds of years; but it has not spread widely. HTLV causes leukaemia in only less than 1% of those infected. The prime mode of transmission of HTLV-1 is between mother and neonate; infections can be reduced by stopping breast-feeding by infected mothers. The isolation of HIV enabled screening tests to be developed for contaminated blood. However, due to the peculiar biology of HIV infection, unfortunately all efforts to develop an effective vaccine have so far failed.

Phase I/II trial of HIV-1 hyperimmune globulin for the prevention of HIV-1 vertical transmission in Uganda

OBJECTIVES

To assess the safety, tolerance, pharmacokinetics, and virologic and immunologic changes associated with the use of Ugandan HIV hyperimmune globulin (HIVIGLOB) in HIV infected pregnant Ugandan women and their infants.

DESIGN

A prospective, phase I/II, three-arm dose escalation trial of HIVIGLOB.

METHODS

HIVIGLOB was prepared from discarded HIV infected units of blood collected from the National Blood Bank in Kampala. From June 1996 to April 1997, 31 HIV positive pregnant women were enrolled with HIVIGLOB infusions given at 37 weeks gestation and within 16 h of birth for infants. The first 10 mother-infant pairs were infused at a dose of 50 mg/kg, followed by 11 pairs at 200 mg/kg, and 10 pairs at 400 mg/kg. Study participants were followed for 30 months.

RESULTS

Thirty-one women and 29 infants were infused with HIVIGLOB. The infusions were safe and well tolerated by the women and their infants at all doses. There were no significant changes in virologic or immunologic parameters after HIVIGLOB infusion. Pharmacokinetic properties of this product were similar to other immune globulin products with a median half-life of 28 days in women and 30 days in infants.

CONCLUSION

An HIV immune globulin product derived from HIV infected Ugandan donors is safe, well tolerated, and has pharmacokinetic properties consistent with other immunoglobulin products. Data suggest that a 400 mg/kg dose of HIVIGLOB would be the most appropriate dose for a subsequent efficacy trial of HIVIGLOB for the prevention of mother to child HIV transmission.

Back to the future: antibody-based strategies for the treatment of infectious diseases

Before antibiotics, sera from immune animals and humans were used to treat a variety of infectious diseases, often with successful results. After the discovery of antimicrobial agents, serum therapy for bacterial infections was rapidly forsaken. In the last two decades, problems with treatment of newly emerged, re-emerged, or persistent infectious diseases necessitated researchers to develop new and/or improved antibody-based therapeutic approaches. This article reviews some information on the use of antibodies for the treatment of infectious diseases, with special reference to the most seminal discoveries and current advances as well as available treatment approaches in this field.

Proposition of treatment to improve the immune response: possible application to AIDS

The molecular similarity between certain human antigenic determinants with those of HIV has been already described. In this matter, we have previously demonstrated, by a chromatographic method, the cross reactivity of human serum albumin with HIV gp 120. The hypothesis that this similarity could be one of the reasons why the virus escapes to the immune system is presented in this paper and a treatment is proposed to enhance the efficiency of the immune response: it is based on the blocking of the determinants of the self, expressed in the thymus, which are in common with the virus. Repeated injections within the thymus of neutralizing antibodies against the pathogen, obtained from a sufficiently distant animal species and purified by affinity chromatography, would prevent the T cells of the host recognizing these epitopes, common to the host and to the virus, from clonal deletion and would improve the immune response.

Longitudinal study of serum neutralization of HIV-1 in infected plasma donors

Earlier studies provided suggestive evidence about the effectiveness of passive immunotherapy for AIDS patients using plasma donated by healthy HIV-1 infected individuals and revealed beneficial effects of plasmapheresis for the immune system of the donors. In this study, anti-HIV-1 neutralizing activity in 31 healthy HIV-1 infected donors of plasma participating in a passive immunotherapy study was investigated as a function of time. Average studied period was 33 months. Using the highly cytopathic HIV-1 NDK strain and MOLT4 cells, it was shown by means of syncytia formation inhibition assay and polyclonal HIV-1 antigen-capture assay that viral neutralizing titers tend either to remain unchanged or increase over time. These findings support the notion that the immune system is not affected adversely in HIV-1 infected plasma donors and lend further support to the feasibility of passive immunotherapy for AIDS patients.

Additive effects characterize the interaction of antibodies involved in neutralization of the primary dualtropic human immunodeficiency virus type 1 isolate 89.6

Human immunodeficiency virus-type I (HIV-1) infection elicits antibodies (Abs) directed against several regions of the gp120 and gp41 envelope glycoproteins. Many of these Abs are able to neutralize T-cell-line-adapted strains (TCLA) of HIV-1, but only a few effectively neutralize primary HIV-1 isolates. The nature of HIV-1 neutralization has been carefully studied using human monoclonal Abs (MAbs), and the ability of such MAbs to act in synergy to neutralize HIV-1 has also been extensively studied. However, most synergy studies have been conducted using TCLA strains. To determine the nature of Ab interaction in HIV-1 primary isolate neutralization, a panel of 12 anti-HIV-1 human immunoglobulin G (IgG) MAbs, specific for epitopes in gp120 and gp41, were used. Initial tests showed that six of these MAbs, as well as sCD4, used individually, were able to neutralize the dualtropic primary isolate HIV-1(89.6); MAbs giving significant neutralization at 2 to 10 microg/ml included 2F5 (anti-gp41), 50-69 (anti-gp41), IgG1b12 (anti-gp120(CD4bd)), 447-52D (anti-gp120(V3)), 2G12 (anti-gp120), and 670-D (anti-gp120(C5)). For studies of reagent interaction, 16 binary combinations of reagents were tested for their ability to neutralize HIV-1(89.6). Reagent combinations tested included one neutralizing MAb with sCD4, six pairs consisting of two neutralizing MAbs, and nine pairs consisting of one neutralizing MAb with another non-neutralizing MAb. To assess the interaction of the latter type of combination, a new mathematical treatment of reagent interaction was developed since previously used methods could be used only when both reagents neutralize. Synergy was noted between sCD4 and a neutralizing anti-gp120(V3) MAb. Antagonism was noted between two pairs of anti-gp41 MAbs (one neutralizing and one non-neutralizing). All of the other 13 pairs of MAbs tested displayed only additive effects. These studies suggest that Abs rarely act in synergy to neutralize primary isolate HIV-1(89.6); many anti-HIV-1 Abs act additively to mediate this biological function.

The role of passive immunization in hiv-positive patients : a case report

An HIV-positive patient presented with pulmonary tuberculosis as her AIDS-defining diagnosis in 1993 and was effectively treated with 12 months of standard antituberculosis medications (isoniazide, rifampin, and pyrazinamide for 2 months). She received zidovudine for 6 weeks at the time of her diagnosis; however, because of patient preference, she has not received subsequent standard HIV medications (7 years). Her CD4 count at the time of diagnosis (1993) was 297/microL. Monthly passive immunotherapy was administered (fresh frozen plasma from HIV-negative blood donors with a significant titer for the anti-vasoactive intestinal peptide [VIP]/NTM antibody) from December 1993 to June 1994. Her CD4 count increased to > 400/microL during the passive immunotherapy and has remained stable for the past 6 years. The rational for the use of anti-VIP/NTM antibodies preparations in HIV, the possible mode of action of anti-VIP/NTM antibodies, the use of Ig preparations, and the role of exercise as a natural source of anti-VIP/NTM antibodies are discussed. This case report supports the potential therapeutic use of anti-VIP antibodies for treatment of HIV disease.

How to prolong the effects of combination therapy for HIV

Infection with HIV leads to AIDS and death in about 90% of patients within ten years. The first generation of anti-HIV drugs inhibited the viral enzyme reverse transcriptase (RT); but long-term studies have revealed side-effects and a high rate of emergence of drug-resistant HIV mutants. The more recent combination of two anti-RT drugs and a protease inhibitor appears to be more promising: approximately 75% of AIDS patients benefit. However, increasing numbers of treatment failures from toxicity and drug-resistant mutants are emerging. Passive immunotherapy (PIT) is a non-toxic form of treatment based on the neutralization of HIV with antibody-rich plasma from healthy HIV-positive individuals. Studies show it can benefit AIDS patients. Here, we suggest that, in combination with anti-HIV drugs, PIT could reduce some of the toxicity of the latter and limit the emergence of drug-resistant HIV strains. In addition, regular plasma donation seems to be beneficial to the donors.

Involvement of the complement system in antibody-mediated post-exposure protection against human immunodeficiency virus type 1

We previously reported that passive transfer of a murine V3-specific monoclonal antibody (BAT123) to hu-PBL-SCID mice challenged with HIV-1LAI confers postexposure protection from infection. The role of the Fc fragment of this antibody as well as the involvement of the complement system in protection were evaluated in vivo. When we compared the postexposure protection offered by BAT123 and CGP 47439, a chimeric form of BAT123 in which the murine Fc domain has been replaced by a human IgG1 Fc domain, CGP 47439 failed to provide postexposure protection against HIV-1LAI despite having similar pharmacokinetics and in vitro neutralizing activity. Furthermore, when hu-PBL-SCID mice were treated with cobra venom factor, which inactivates serum complement activity, the postexposure protective ability of BAT123 was abrogated. These findings suggest that the complement system is involved in the passive protection against HIV-1 infection conferred by the murine monoclonal antibody BAT123 in hu-PBL-SCID mice.

Potent and synergistic neutralization of human immunodeficiency virus (HIV) type 1 primary isolates by hyperimmune anti-HIV immunoglobulin combined with monoclonal antibodies 2F5 and 2G12

Three antibody reagents that neutralize primary human immunodeficiency virus type 1 (HIV-1) isolates were tested for magnitude and breadth of neutralization when used alone or in double or triple combinations. Hyperimmune anti-HIV immunoglobulin (HIVIG) is derived from the plasma of HIV-1-infected donors, and monoclonal antibodies (MAbs) 2F5 and 2G12 bind to distinct regions of the HIV-1 envelope glycoprotein. The antibodies were initially tested against a panel of 15 clade B HIV-1 isolates, using a single concentration that is achievable in vivo (HIVIG, 2,500 microg/ml; MAbs, 25 microg/ml). Individual antibody reagents neutralized many of the viruses tested, but antibody potency varied substantially among the viruses. The virus neutralization produced by double combinations of HIVIG plus 2F5 or 2G12, the two MAbs together, or the triple combination of HIVIG, 2F5, and 2G12 was generally equal to or greater than that predicted by the effect of individual antibodies. Overall, the triple combination displayed the greatest magnitude and breadth of neutralization. Synergistic neutralization was evaluated by analyzing data from dose-response curves of each individual antibody reagent compared to the triple combination and was demonstrated against each of four viruses tested. Therefore, combinations of polyclonal and monoclonal anti-HIV antibodies can produce additive or synergistic neutralization of primary HIV-1 isolates. Passive immunotherapy for treatment or prophylaxis of HIV-1 should consider mixtures of potent neutralizing antibody reagents to expand the magnitude and breadth of virus neutralization.

Can repeated plasma donation by asymptomatic HIV-infected individuals delay the onset of AIDS?

Healthy HIV-positive regular donors of plasma in a programme of passive immunotherapy for AIDS patients were studied over a period of about two years. None developed symptoms of clinical progression; most seemed to make substantial gains of CD4 cells by comparison with asymptomatic individuals who were not donating. The effects of donation did not seem to diminish with repetition, and donor CD4 counts tended towards stabilizing within normal limits. Asymptomatic HIV-positive individuals were compared immunologically with 'normals' and people with AIDS, using a battery of 25 measurements on peripheral blood. The immunological profiles of donor and non-donor asymptomatics, indistinguishable at the start, became dissimilar: donors' profiles resembled AIDS less, non-donors became less like 'normal' and a few non-donor results could not be distinguished from AIDS. Improvement in the CD4 counts and amelioration of the immunological profile in donors provide prima facie evidence that plasmapheresis may be therapeutic for asymptomatic HIV-positive people. Further studies are justified.

Pharmacokinetics of hyperimmune anti-human immunodeficiency virus immunoglobulin in persons with AIDS

Hyperimmune anti-human immunodeficiency virus immunoglobulin (HIVIG) is an intravenous immunoglobulin prepared from HIV-infected asymptomatic donors with a CD4 cell count greater than 400 cells/microl and a high titer of antibody to HIV-1 p24 protein. Twelve persons with AIDS received four doses of HMG (two at 50 mg/kg of body weight and then two at 200 mg/kg) every 28 days. Pharmacokinetics were evaluated by measurement of anti-p24 antibody. HIVIG was well tolerated, and all participants completed the study. Three subjects who were not receiving Pneumocystis carinii pneumonia (PCP) prophylaxis developed PCP. The mean value for HIVIG clearance was 3.02 ml/kg/day at 50 mg/kg and 3.65 ml/kg/day at 200 mg/kg (P = 0.027); the mean trough antibody titers (reciprocal units) were 1,442 and 4,428, respectively. This study indicates that high titers of anti-p24 antibody can be maintained with a monthly administration schedule of HIVIG and that short-term safety is acceptable. Comparisons to evaluate the therapeutic potential of HIVIG are justified.

Use of intravenous immunoglobulin to prevent or treat infections in persons with immune deficiency

Intravenous immunoglobulin (IVIG) concentrates were originally developed as replacement therapy for individuals with primary deficiencies of the immune system. However, in various well-designed, controlled clinical trials, the ability of IVIG to prevent and possibly treat infections in patients with secondary immune deficiencies has also been considered. In this review, we briefly consider these different applications and suggest whether the data are sufficient to employ IVIG in these clinical settings.

Syncytium-inhibiting and neutralizing activity in maternal sera fail to prevent vertical transmission of human immunodeficiency virus type 1

OBJECTIVES

To measure the prevalence and titers of syncytium-inhibiting (SI) and neutralizing (Nt) antibodies to HIV-1 in mothers' blood close to the time of delivery and to correlate such findings with the infection status of their offspring.

METHODS

We analyzed serum specimens from a convenience sample of 22 HIV-infected mothers. The HIV-1 infection status of their children was determined. Forty-five percent of the women transmitted and 55% did not transmit infection to their offspring. Cord blood samples from offspring of the mothers were also studied. We measured maternal SI antibody titers against cells infected with HIV-1/SB, a strain isolated from a transmitting mother in New Haven, as well as cells infected with the more prevalent MN strain of HIV-1. We compared SI antibody titers to the SB strain in 11 matched maternal and cord blood samples. Nt antibody titers to HIV-1/SB were also measured in 20 maternal sera.

RESULTS

Using the SB and MN strains of HIV-1, we found no difference in the prevalence or titer of SI antibody in the sera of transmitting and nontransmitting mothers. Only 35% of samples were concordant for presence or absence of SI antibody to the two strains. Furthermore the presence or absence of SI antibody in cord blood did not correlate with virus transmission. Both the frequency and titer of Nt antibody to HIV-1/SB were higher in the sera of mothers who transmitted infection when compared to those who did not. Only one-half of maternal blood samples were concordant for either the presence or absence of SI and Nt antibodies.

CONCLUSIONS

We could not demonstrate a correlation between the presence of two types of functional antibodies (i.e. SI and Nt) to HIV-1 in the sera of pregnant women and vertical transmission. Efforts to induce or to increase such antibodies in infected mothers by immunization with vaccines or hyperimmune globulins may not alter the risk of vertical transmission.

Passive immunotherapy for retroviral disease: influence of major histocompatibility complex type and T-cell responsiveness

Administration of virus-specific antibodies is known to be an effective early treatment for some viral infections. Such immunotherapy probably acts by antibody-mediated neutralization of viral infectivity and is often thought to function independently of T-cell-mediated immune responses. In the present experiments, we studied passive antibody therapy using Friend murine leukemia virus complex as a model for an immunosuppressive retroviral disease in adult mice. The results showed that antibody therapy could induce recovery from a well-established retroviral infection. However, the success of therapy was dependent on the presence of both CD4+ and CD8+ T lymphocytes. Thus, cell-mediated responses were required for recovery from infection even in the presence of therapeutic levels of antibody. The major histocompatibility type of the mice was also an important factor determining the relative success of antibody therapy in this system, but it was less critical for low-dose than for high-dose infections. Our results imply that limited T-cell responsiveness as dictated by major histocompatibility genes and/or stage of disease may have contributed to previous immunotherapy failures in AIDS patients. Possible strategies to improve the efficacy of future therapies are discussed.

Passive immunotherapy in AIDS: a double-blind randomized study based on transfusions of plasma rich in anti-human immunodeficiency virus 1 antibodies vs. transfusions of seronegative plasma

A randomized double-blind controlled trial was conducted to determine the efficacy of passive immunotherapy in the treatment of symptomatic human immunodeficiency virus (HIV) infection. This trial included 86 symptomatic patients randomized to receive plasma rich in anti-HIV-1 antibody or standard seronegative plasma. Each patient in both groups received a 300-ml infusion every 14 days over a 1-year period, and every 28 days thereafter, in addition to zidovudine and other conventional prophylactic treatments. Plasma donors were selected among symptomless seropositive individuals with a CD4 lymphocyte count > or = 400 x 10(6) cells per liter, a negative p24 antigen assay, and a high concentration of anti-p24 antibody. The plasmas were heat-inactivated before infusion. During the study period (day 28-day 365) scheduled by the protocol, clinical benefit from passive immunotherapy was observed in delaying the appearance of the first AIDS-defining event (P < 0.009) and reducing the cumulative incidence of such events, which was estimated 3-fold higher in the control group compared to the treatment group. Seven deaths occurred in the treatment group vs. 11 in the control group (P = 0.27). A total of 47 patients died or exhibited new AIDS-defining events, 18 in the treatment group and 29 in the control group (P = 0.009). No clinical benefit was observed after the 1-year period with infusions performed every 4 weeks. These results indicate a favorable effect of passive immunotherapy on the evolution of advanced AIDS.

Does intravenous immune globulin have a role in HIV-infected patients?

The main immunological abnormality in human immunodeficiency virus (HIV)-infected patients, and particularly those with the acquired immune deficiency syndrome (AIDS), is a deficiency in cellular immunity. However, symptomatic HIV-infected children also have evidence of deficiency of specific antibody synthesis, and intravenous immune globulin (IVIG) preparations in doses of 0.2-0.4 g/kg every 2-4 weeks have been shown to reduce the incidence of respiratory infections. IVIG therapy may also reduce the mortality and incidence of bacterial infections in adults but further studies are required. In addition, high-dose IVIG therapy (1-2 g/kg over 2-5 days) produces increased platelet counts in patients with idiopathic thrombocytopenic purpura (ITP) associated with HIV infection. Finally, IVIG therapy may have a role in HIV-infected patients suffering from severe parvovirus B19 or measles infection, or in patients suffering from autoimmune disorders where high-dose IVIG therapy has been shown to be efficacious.

Passive immunization of macaques against SIV infection

Passive immunization with plasma from an inactivated-whole SIVmac vaccine protected monkey conferred complete or partial protection to rhesus macaques challenged intravenously 4 or 18 hours later with 10 AID50 of homologous cell-free virus. In contrast, passive immunization with inactivated plasma or purified immunoglobulin (Ig) from SIVmac infected asymptomatic monkeys failed to protect any recipients similarly challenged and may have enhanced infection and accelerated disease. Administered 24 hours post challenge, anti-SIV Ig may also have enhanced the infection.

A potent, neutralizing human monoclonal antibody against a unique epitope overlapping the CD4-binding site of HIV-1 gp120 that is broadly conserved across North American and African virus isolates

A human monoclonal antibody (HuMAb), 5145A, against HIV-1 gp120 was isolated from an asymptomatic, seropositive hemophiliac. The epitope of this HuMAb was destroyed by reduction of gp120 disulfide bonds, but not by removal of N-linked carbohydrates. This epitope overlaps the CD4-binding site of gp120, because binding of 5145A to gp120 is inhibited by soluble CD4 and by 1125H, a previously described HuMAb directed toward the CD4-binding site. However, the 5145A epitope differs from those of 1125H and other anti-CD4-binding site HuMAbs previously described, as documented by the viral strain specificity of 5145A and its reactivity with a panel of gp120 mutants. Specifically, 5145A reacted with 14 of 15 HIV-1 isolates tested, including 9 isolates from the Central African Republic, 6 of which were not recognized by 1125H. Partial epitope mapping of 5145A, using a series of gp120 mutants, demonstrated its lack of sensitivity to mutations in residues 257 and 427, contrasting with a marked sensitivity to mutations in residues 368 and 370. This pattern of reactivity distinguishes its epitope from that of any HuMAb against the CD4-binding site region described to date. In addition, 5145A exhibited potent and essentially equivalent neutralization of the MN, SF-2, IIIB, and RF strains and possessed significant neutralizing activity against three of three African strains tested. Finally, 5145A synergistically neutralized the MN and SF-2 strains of HIV-1 when combined with 4117C, a HuMAb against the V3 loop. The broad strain specificity and potent neutralizing activity of 5145A, together with its ability to synergize with an anti-V3 loop HuMAb in neutralizing HIV-1, indicate that 5145A has excellent potential as a passive immunotherapeutic agent against HIV-1.

Pharmacokinetics of an HIV-1 gp120-specific chimeric antibody in patients with HIV-1 disease

The pharmacokinetics of mouse V/human C (gamma 1, kappa) chimeric monoclonal antibody CGP 47 439 specific for the principal neutralizing determinant of human immunodeficiency virus type 1 (HIV-1) was studied in patients with stage IV HIV-1 disease in an open-labeled phase I/IIA trial. Twelve male patients were enrolled and nine completed the study. Patients were divided into three groups according to the extent of CGP 47 439 to bind to gp120 from their viral isolates: undetectable for group 1, modestly reactive for group 2, and strongly reactive for group 3. A first dose of 1, 10, or 25 mg was administered by intravenous infusion to group 1, group 2 and group 3 patients, respectively. The patients then received seven doses of 50, 100, or 200 mg, respectively, every three weeks. CGP 47 439 serum concentrations were determined by an ELISA using monoclonal antibody AB19-4 specific for the idiotope of CGP 47 439. Half an hour after infusion only 25.5-36.1% of the administered antibody was found in the serum, reflecting its rapid distribution in the extravascular space and possibly binding to gp120 antigen in some of the patients. The terminal elimination half-life (T1/2) was 16.2 days in group 1 patients, 9.7 days in group 2 and in group 3 patients 7.5 days and 9.1 days. An antibody response to CGP 47 439 was not a factor in determining elimination rates, because only very low and transient responses were found in three patients. These results suggest that the reactivity of CGP 47 439 with HIV-1 gp120 contributed to its elimination in HIV-1 infected patients.

Mouse/human chimeric anti-HIV-1 gp120 antibody to the principal neutralizing determinant: tolerability and pharmacokinetics in cynomolgus monkeys, Macaca fascicularis

In preparing for testing a pharmaceutical grade preparation of chimeric (mouse/human) antibody CGP 47,439 in HIV-1 infected individuals, it was administered to Macaca fascicularis (cynomolgus) monkeys to study tolerability, immunogenicity and pharmacokinetics. Four groups of monkeys, three males and three females per group, received respectively four infusions of 0, 1.43, 4.3, and 14.3 mg of CGP 47,439/kg body weight at one-week intervals. The chimeric antibody induced no fever, was tolerated well throughout the 50-day observation period, elicited no tissue damage and no anti-antibody response. The pharmacokinetic profile was similar at all dose levels with a mean T1/2 alpha of 14.2 h (range 11.8-19.3 h) and a mean T1/2 beta of 172.6 h (range 137.2-220.5h). Following four successive antibody infusions serum concentrations of CGP 47,439 increased without reaching a steady state, and its measured concentrations were comparable to the simulated values. Collectively the study has provided safety and pharmacokinetic data that would allow human studies with this antibody in AIDS patients.

Discovery of antibodies

Passive immunisation has been used in clinical practice since the end of last century, mainly for prophylaxis. Success of early treatments was marred by anaphylactic reactions and serum sickness because antibodies or antitoxins were not raised in humans. Recombination of gene segments during antibody synthesis means that specific antibodies for numerous antigens can be produced from a limited gene pool. Killer lymphocytes, phagocytes, and complement then bind to the constant region of the antibody facilitating elimination of the pathogen. Development of a method of obtaining large quantities of antibodies against a specific antigen (monoclonal antibodies) offers the possibility of initiating host defence mechanisms against any unwanted antigen, though some problems still remain in preventing the body from attacking the monoclonal antibody.

Serum antibodies to HIV-1 in recombinant vaccinia virus recipients boosted with purified recombinant gp160. NIAID AIDS Vaccine Clinical Trials Network

Serum antibody responses were studied in detail in four vaccinia-naive volunteers in a phase I trial evaluating primary vaccination with a recombinant vaccinia virus expressing the HIV-1 gp160 envelope glycoprotein (HIVAC-1e, Oncogen/Bristol-Myers Squibb), followed by booster immunization with baculovirus-derived rgp160 (VaxSyn, MicroGeneSys). Prior to boosting, low-titer Fc receptor (FcR)-mediated, antibody-dependent enhancing (ADE) activity was detected in two of four volunteers but no IgM, IgG, IgA, neutralizing activity, or complement-mediated ADE activity was detected. Two weeks after boosting, all four volunteers developed HIV-1-specific IgG with titers of 1:160 to 1:640 by immunofluorescence assay. IgG1 was present in sera from each individual, while IgG2 and IgG3 were present in sera from two individuals, and IgG4 was present in serum from one individual. IgM and IgA were undetectable in all sera. Only one volunteer had IgG to the heterologous HIV-1 isolates, RF, MN, and SF2, after boosting. Serum from this volunteer neutralized the vaccine strain, LAV/IIIB, but not the heterologous strains, RF, MN, and SF2. Antibodies from the remaining volunteers had no neutralizing activity. The neutralizing serum had a positive reaction in a peptide-based ELISA utilizing a peptide corresponding to the principal neutralizing domain of the third hypervariable region (i.e., V3 loop) of the envelope glycoprotein. Neutralizing activity was partially removed by adsorption to this peptide, suggesting that it contained a type-specific neutralizing vaccine epitope. A low titer (1:40 to 1:80) of complement-mediated ADE activity to HIV-1 IIIB was present in sera from three vaccinees after boosting. FcR-ADE activity for HIV-1 SF2 and SF-128A were present in sera from two of these three vaccinees. None of the volunteers developed antisyncytial antibodies. These results indicate that inoculation with recombinant vaccinia followed by rgp160 boosting is the most effective strategy to date for inducing serum antibodies to the envelope glycoproteins of HIV-1, but further study is needed to optimize the functionality and cross-reactivity of these responses.

Characterization of a mouse/human chimeric monoclonal antibody (C beta 1) to a principal neutralizing domain of the human immunodeficiency virus type 1 envelope protein

A chimeric mouse-human antibody (C beta 1) was constructed that recognized the principal neutralizing domain (PND) of human immunodeficiency virus type 1 (HIV-1) gp120. The constant (C) immunoglobulin regions (C gamma 1 and C kappa) of a mouse monoclonal antibody, 0.5 beta, were substituted for the human C gamma 1 and C kappa by recombining the DNA modules encoding variable or C regions. The DNA constructs were then transfected into X63 Ag8.653 myeloma cells. A clone with a high production of the chimeric antibody (C beta 1) was selected. This antibody was tested for its biological activity against HIV-1. It bound to the surface of HTLV-IIIB-infected cells and reacted with gp120/160 with equal affinity and specificity to that of the parental 0.5 beta murine monoclonal antibody in a Western blot assay. Neutralization and/or enhancement of HIV infection were evaluated with C beta 1 and 0.5 beta. Both C beta 1 and 0.5 beta neutralized cell-to-cell infection and cell-free virus infection by HTLV-IIIB. Antibody-dependence enhancement of HIV infection was not observed with either C beta 1 or 0.5 beta in the presence or absence of human complement. Antibody-dependent cell-mediated cytolysis (ADCC) and antibody-dependent complement-mediated cytolysis (ACC) were observed with C beta 1 but not with the parental 0.5 beta. These findings suggest that the neutralizing antibodies to PND may neutralize but not enhance HIV infection. Furthermore, the high levels of ACC and ADCC shown against HIV-infected cells by C beta 1 indicate that the clinical application of such monoclonal antibodies may be possible.

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.

Anti-idiotype monoclonal antibody elicits broadly neutralizing anti-gp120 antibodies in monkeys

Murine monoclonal antibodies (mAbs) were raised against human, polyclonal, anti-gp120 antibodies (Ab1) and were selected for binding to broadly neutralizing anti-gp120 antibodies in sera positive for human immunodeficiency virus (HIV). One anti-idiotype mAb (Ab2), 3C9, was found to be specific for human anti-gp120 antibodies directed against an epitope around the conserved CD4 attachment site of gp120. The 3C9 reactive human anti-gp120 antibodies (3C9+ Ab) neutralized MN, IIIB, RF, and four primary isolates of HIV type 1 (HIV-1). Cynomolgus monkeys were immunized with 3C9 in adjuvant to test whether this anti-idiotype mAb could induce neutralizing anti-gp120 antibodies. The results show that purified anti-anti-idiotype antibodies (Ab3) from 3C9 immune sera bind to an epitope around the CD4 attachment site of gp120SF and gp120IIIB. Furthermore, purified gp120-specific Ab3 neutralize MN, IIIB, and RF isolates. These results demonstrate that primates immunized with an anti-idiotype mAb produce broadly neutralizing anti-HIV-1 antibodies. Since this anti-idiotype mAb was selected by identifying a clonotypic marker, its biological activity can be explained as the results of clonotypic B-cell stimulation.

Identification and characterization of a neutralization site within the second variable region of human immunodeficiency virus type 1 gp120

Two monoclonal antibodies designated BAT085 and G3-136 were raised by immunizing BALB/c mice with gp120 purified from human immunodeficiency virus type 1 (HIV-1) IIIB-infected H9 cell extracts. Among three HIV-1 laboratory isolates (IIIB, MN, and RF), BAT085 neutralized only IIIB infection of CEM-SS cells, whereas G3-136 neutralized both IIIB and RF. These antibodies also neutralized a few primary HIV-1 isolates in the infection of activated human peripheral blood mononuclear cells. In indirect immunofluorescence assays, BAT085 bound to H9 cells infected with IIIB or MN, while G3-136 bound to H9 cells infected with IIIB or RF, but not MN. Using sequence-overlapping synthetic peptides of HIV-1 IIIB gp120, the binding site of BAT085 and G3-136 was mapped to a peptidic segment in the V2 region (amino acid residues 169 to 183). The binding of these antibodies to immobilized gp120 was not inhibited by the antibodies directed to the principal neutralization determinant in the V3 region or to the CD4-binding domain of gp120. In a competition enzyme-linked immunosorbent assay, soluble CD4 inhibited G3-136 but not BAT085 from binding to gp120. Deglycosylation of gp120 by endo-beta-N-acetylglucosaminidase H or reduction of gp120 by dithiothreitol diminished its reactivity with G3-136 but not with BAT085. These results indicate that the V2 region of gp120 contains multiple neutralization determinants recognized by antibodies in both a conformation-dependent and -independent manner.

Strategies in the treatment of AIDS and related diseases: the lessons of cancer chemotherapy

The replication cycle of human immunodeficiency virus type 1 (HIV-1) consists of four distinct stages, each of which can be targeted for specific antiviral chemotherapy. The stages are (1) the attachment of virus to the CD4 receptor at the cell surface; (2) the uncoating of viral nucleic acid and its conversion via viral reverse transcriptase activity to DNA; (3) cellular multiplication, accompanied by the replication of integrated proviral DNA and production of viral RNA and proteins; and (4) the assembly and liberation of progeny virus from the cell and the potential reinitiation of the replication cycle in previously uninfected cells. Since each of these steps represents a potential target for anti-HIV chemotherapy, it is apparent that the rationale for the use of antiviral drugs is not dissimilar from the manner in which antineoplastic agents are targeted to specific stages in the replication cycle of tumor cells. As in the case of anticancer chemotherapy, it is hoped that combinations of drugs, which act against different steps in the viral replication cycle, might have synergistic potential. AZT or zidovudine is the most widely used drug to date to impede the replication of HIV-1; it is significant that this compound was designed initially with anticancer chemotherapy in mind. Although AZT therapy has been reasonably successful, this drug has had important toxic side effects. As in the case of many cancer chemotherapeutic agents, drug resistance to AZT is likely to be an important problem, and there have been several reports of the isolation of drug-resistant variants of HIV-1.

Pharmacokinetics, toxicity, and activity of intravenous dextran sulfate in human immunodeficiency virus infection

Polysulfated polysaccharides are attractive candidates for antiviral drug development because of their potent in vitro activities against human immunodeficiency virus (HIV), herpesviruses, and other enveloped viruses. To determine the potential anti-HIV activity of a prototypical polysulfated polysaccharide, we administered the maximally tolerated dose of dextran sulfate by continuous intravenous infusion to 10 subjects with symptomatic HIV infection for up to 14 days. Since parenteral dextran sulfate is an anticoagulant, the infusion was adjusted to produce the greatest acceptable increase in activated partial thromboplastin time. Drug concentrations in plasma achieved with this protocol were up to 200-fold greater than the 50% inhibitory concentration for free HIV infectivity in vitro. Despite this, circulating HIV antigen (p24) levels increased in all eight subjects who received the drug for more than 3 days (median proportional increase, 73.5%; range, 32 to 130%); this increase was highly significant when it was compared with that in a large cohort of untreated historical controls (Fisher's exact test, P less than 0.001). Frequent decreases in infusion rate were required in all subjects to maintain a constant activated partial thromboplastin time; plasma dextran sulfate levels did not fall as the infusion rate decreased, suggesting a decline in estimated drug clearance over time. Continuous intravenous dextran sulfate was toxic, producing profound but reversible thrombocytopenia in all eight subjects who received drug for more than 3 days and extensive but reversible alopecia in five of these subjects. Because of its toxicity and lack of beneficial effect on surrogate markers, dextran sulfate is unlikely to have a practical role in the treatment of symptomatic HIV infection.