Technical challenges facing therapeutic cancer vaccines

Significant advances have been made in the development of therapeutic cancer vaccines, with vaccines for renal, colorectal and prostate cancers showing real promise. This review describes progress in the development of cellular vaccines, along with the technical challenges that have to be overcome to bring these vaccines to phase III clinical trials and commercial supply. The issues of large-scale vaccine design and production, the problems associated with scaling up, and the assessment of quality and yield are discussed. Regulatory guidelines for the production of cellular vaccines that have evolved alongside the technology for vaccine production over the last few years are also reviewed.

Overcoming technical challenges in the development of cancer vaccines

Cancer vaccines have been developed using a wide range of technologies, yielding agents ranging from nonspecific immunostimulants through to highly technical peptide- and DNA-based candidates. There are many technical challenges involved in even the most basic decisions in vaccine development, such as the choice of antigen, formulation, adjuvant, route of delivery and schedule. However, as discussed in this feature review, the tumor itself may pose the greatest technical challenge, particularly with regard to escaping the immune response. Strategies to overcome this challenge are discussed.

13-cis-Retinoic acid in combination with gemcitabine in the treatment of locally advanced and metastatic pancreatic cancer--report of a pilot phase II study

AIMS

Adenocarcinoma of the pancreas is a cancer with extremely poor prognosis and limited therapeutic options. Retinoids are derivatives of vitamin A involved in the control of many biological functions, including cell growth and differentiation and the induction of apoptosis. On the basis of pre-clinical evidence and some clinical data, we conducted a phase II study of 13-cis-retinoic acid (13-cis-RA) in combination with gemcitabine in patients with unresectable pancreatic carcinoma.

MATERIALS AND METHODS

Patients with histologically confirmed unresectable pancreatic carcinoma were treated with gemcitabine 1000 mg/m2 on days 8, 15, 22 plus 13-cis-RA 1 mg/kg on days 1-14 for six cycles. The end points included the objective response rate and median survival.

RESULTS

Thirty patients were recruited, 15 men and 15 women; 20 patients were evaluable. The median age was 65 years (range 44-79 years) and the median Karnofsky performance status was 80% (range 60-100%). The median follow-up was 21 months. One patient achieved a partial remission, seven patients had stable disease and 12 patients developed progressive disease. Toxicity was mainly haematological, with eight cases of grade 3 and four cases of grade 4 neutropenia, thrombocytopenia and anaemia. The median survival was 7.8 months (range 2.6-21.6 months).

CONCLUSIONS

The combination of gemcitabine and 13-cis-RA was well tolerated, but we did not see improvement in the response rate. Further studies with other retinoids may be beneficial to patients with unresectable pancreatic cancer.

Biomarkers for the development of cancer vaccines: current status

Significant improvements in our knowledge of tumor immunology have resulted in more sophisticated vaccine approaches for the treatment of cancer. However, research into biomarkers that correlate with the clinical outcome of immunotherapy has lagged behind vaccine development. To this extent, very few immunological or other markers exist that can be used in clinical trials for immunotherapy. In this review, we discuss the current status of biomarker development specifically for the monitoring and development of cancer vaccines. This includes immunological biomarkers (measurement of T-cell and cytokine responses), autoimmunity as a correlate for treatment outcome, and the possible development of multiple biomarkers using high-throughput proteomics technologies. The generation of such biomarkers will allow us to make clinical decisions about patient treatment at an earlier stage and should aid in shortening the development time for vaccines.

Tumor antigens as surrogate markers and targets for therapy and vaccines

There are a large number of tumor antigens, which may either be specific to the tumor or inappropriately expressed or processed (tumor-associated antigen, TAA). Over the last few years, hundreds of new TAAs have been identified. Some of these represent good targets for both passive (antibody based) and active (vaccine based) therapies. Antibody treatments targeted on tumor-specific antigens, such as Herceptin and Cetuximab, have been effective in clinical trials and are now licensed. In addition, TAAs act as good surrogate markers for use in both the diagnosis and assessment of treatment in cancer patients.

Biomarkers for development of cancer vaccines

The search for molecules that correlate with cancer progression is an evolving and exciting area of research. Such biomarkers have utility in a number of areas, most notably in a variety of clinical development programs. Modern technologies are revealing multiple potential biomarker candidates. However, the challenge remains in validating the correlation in levels of a particular molecule with clinical parameters. In this article, the area of biomarkers and cancer vaccines is briefly reviewed and the possibility of combining multiple molecules to generate a profile that correlates with outcome, rather than using more conventional single molecule biomarker systems, is explored.

Immunotherapy of murine prostate cancer using whole tumor cells killed ex vivo by herpes simplex viral thymidine kinase/ganciclovir suicide gene therapy

Whole cell cancer vaccines are currently under clinical evaluation. Their immunogenicity may depend on the mode of death of the vaccine cells prior to uptake by professional antigen-presenting cells and crosspriming of T cells. Destruction of tumor in vivo by genetic prodrug activation therapy leads to a marked local and systemic immune response, local T-cell infiltration and the establishment of T-cell memory. We postulated that this immunostimulation may be due to induction of danger signals and the inherent immunogenicity of products of HSVtk/ganciclovir kill. Using established models of murine prostate cancer, we have evaluated the efficacy of anti-tumor vaccines comprising irradiated allogeneic or autologous whole cells expressing HSVtK, which are first killed in vitro by prodrug activation using ganciclovir. HSVtk/ganciclovir-induced cell kill was through the induction of apoptosis. The vaccine was found to be effective in both models and superior to traditional irradiated whole tumor cells even after single doses. Protection against tumor challenge was associated with marked proliferative and Th1 cytokine responses. This approach would be applicable clinically in terms of ease of vaccine production, safety, storage and avoidance of potential toxicities of in vivo gene transfer.

Accumulation of Krebs cycle intermediates and over-expression of HIF1alpha in tumours which result from germline FH and SDH mutations

The nuclear-encoded Krebs cycle enzymes, fumarate hydratase (FH) and succinate dehydrogenase (SDHB, -C and -D), act as tumour suppressors. Germline mutations in FH predispose individuals to leiomyomas and renal cell cancer (HLRCC), whereas mutations in SDH cause paragangliomas and phaeochromocytomas (HPGL). In this study, we have shown that FH-deficient cells and tumours accumulate fumarate and, to a lesser extent, succinate. SDH-deficient tumours principally accumulate succinate. In situ analyses showed that these tumours also have over-expression of hypoxia-inducible factor 1alpha (HIF1alpha), activation of HIF1alphatargets (such as vascular endothelial growth factor) and high microvessel density. We found no evidence of increased reactive oxygen species in our cells. Our data provide in vivo evidence to support the hypothesis that increased succinate and/or fumarate causes stabilization of HIF1alpha a plausible mechanism, inhibition of HIF prolyl hydroxylases, has previously been suggested by in vitro studies. The basic mechanism of tumorigenesis in HPGL and HLRCC is likely to be pseudo-hypoxic drive, just as it is in von Hippel-Lindau syndrome.

Immunotherapy of murine prostate cancer using whole tumour cells killed ex vivo by cytosine deaminase/5-fluorocytosine suicide-gene therapy

OBJECTIVE

To evaluate the efficacy of antitumour vaccines comprising irradiated allogeneic or autologous whole cells expressing cytosine deaminase (CD) which are first killed ex vivo by prodrug activation using 5-fluorocytosine (5-FC), as the immunogenicity of tumour cells used as irradiated vaccines depends both on antigen expression and on the mode of their death.

MATERIALS AND METHODS

The PA3 rat prostate cell line and MATLyLu, an androgen-insensitive subline, were grown and transfected with CD (designated PCD and MCD). In vitro drug-sensitivity was assessed in the cell lines using a viability assay, and the mode of cell death quantified by assessing apoptosis. Bax and bcl-2 expression were assessed by Western blot analysis. For in vivo experiments, male 8-10-week-old Lobund-Wistar rats were vaccinated (using vehicle in control groups) with 5 x 10(6) cells, all cells being irradiated before injection, to give groups with PA3, PCD, PCD killed with 5-FC, MatLyLu, MCD, and MCD killed with 5-FC. After 7 days all animals were given a subcutaneous tumour challenge of PA3 cells, and tumour volume measured subsequently. Immune responses were assessed in splenocytes.

RESULTS

The efficiency of cell kill varied between the cell lines assessed, but cell death was by induced apoptosis. Single doses of vaccine were most effective in the allogeneic setting, causing significantly slower growth of syngeneic tumour challenge (P < 0.01), and 25% better survival at 50 days (P < 0.02) than irradiated untransfected cells. This was consistent with the greater proliferative response after allogeneic than autologous vaccination.

CONCLUSION

The immunogenicity of irradiated tumour cells is enhanced when they are killed ex-vivo using suicide-gene therapy. This approach would be clinically applicable in terms of ease of vaccine production, safety, storage and avoidance of potential toxicities of in vivo gene transfer.

Novel strains of Salmonella typhimurium as potential vectors for gene delivery

DNA vaccines are known to induce long-term antigen specific cellular responses. We tested two new strains of Salmonella typhimurium, one carrying a mutation in a SPI-2 gene and the aroC-gene and another carrying mutations in the sifA- and aroC-genes, as potential DNA vaccine delivery vehicles. We compared them with the SL7207 strain and found that the new strains were more invasive, and that they were efficient mediators of gene transfer in vitro using EGFP as reporter gene. We tested the ability of the new strains to survive within the spleen, liver and mesenteric lymph nodes and evaluated their safety in C57/BL/6J mice.

Novel immunotherapeutic approaches to prostate cancer

Immunotherapy offers new and exciting therapeutic options for patients with late-stage prostate cancer. While the concept of using the immune system to combat cancer is not new, it is only in this post-genomics era that the realistic possibility exists of effectively harnessing the immune system against disease. Immunotherapies can be loosely divided into three major categories: non-specific immune stimulation, specific target antigens and whole-cell approaches. All three systems have merits and drawbacks, although the goal of overcoming 'self' tolerance is common to all of them. This review highlights some of the more recent experiments in each of these three fields, focusing particularly on prostate cancer. We suggest that it is unlikely that one single cancer antigen exists and that recent data support this by showing that strong immune responses to prostate antigens can be elicited in a variety of ways. Therefore, a multivalent approach is likely to be most clinically efficacious. Data gathered from the past three years are discussed in this review and lead to the inescapable conclusion that immunotherapy is now a reality.

Cryopreserved dendritic cells for intratumoral immunotherapy do not require re-culture prior to human vaccination

Dendritic cell (DC) immunotherapy for cancer has shown great promise so far. The ability to deliver dendritic cells directly into tumours where they are capable of acquiring tumour antigens prior to stimulating specific T cell responses has been demonstrated both in animal models and human patients. Clinical grade DCs can be grown from peripheral blood monocytes in the absence of foetal calf serum (FCS) and cryopreserved to generate plentiful identical aliquots thus avoiding repeated venesection. However, the approach is still limited by the necessity to return thawed DCs to culture prior to injection. It would be more advantageous to directly inject the DCs whilst still in the freezing medium and thus prevent the need for further manipulation. Whilst several reports have shown that cryopreserved DCs can survive for over 72 h when returned to culture, there is no information regarding the longevity of cells maintained in the freezing medium after thawing. In this report we have shown that DCs may remain in freezing medium for up to 1 h without affecting their survival, phenotype or function. This period of time is sufficient to allow for any delays incurred between the preparation of the DCs and time taken to be administered within a standard clinical setting. This study demonstrates that clinical grade DCs can be cryopreserved and thawed whilst retaining the ability to acquire exogenous antigenic material required for intratumoural immunotherapy. The survival of these cells within the freezing medium without the requirement for re-culture expands their availability for administration directly to the tumours of patients in non-specialist centres that do not have the appropriate facilities for DC re-culture.

The common heat shock protein receptor CD91 is up-regulated on monocytes of advanced melanoma slow progressors

Despite advances in our understanding of tumour immunology there is no therapy of proven survival benefit for advanced melanoma. Nevertheless, disease progression is slow in a small proportion of patients with metastatic melanoma, suggesting a contribution to outcome from host factors. Recent data have indicated the importance of the heat shock protein receptor CD91 in immune responses to, and progression of, infectious disease. Here we investigate the relationship between CD91 expression and outcome in malignancy. Rare melanoma patients were recruited with advanced disease that was progressing unusually slowly. CD91 expression on their monocytes was compared with control patients with more typical rapidly advancing metastatic disease. Th1 and Th2 cytokines, as well as innate and adaptive immune subsets, were also measured in the two groups. A significant increase in median CD91 expression levels was observed in slow progressors (P = 0.006). There were no differences in other immune subset markers or inflammatory cytokines. The ability of CD91 to internalize and cross-present tumour antigens through the major histocompatibility complex class I pathway may maintain CD8-positive cytotoxic T cell responses and contribute to slow progression of advanced melanoma.

Differential expression of melanoma-associated antigens and molecules involved in antigen processing and presentation in three cell lines established from a single patient

Tumour cells are able to evade the immune system by using several 'escape mechanisms'. Downregulation of molecules involved in the processing and presentation of self-antigens has been reported. However, these adaptations have not been compared in metastases in different anatomical locations but derived from a single patient. We investigated three melanoma cell lines--MJT1 from the parietal lobe of the brain, MJT3 from the cerebellum and MJT5 from the left side of the neck--established from biopsies excised from a 45 year old female patient. Although human leukocyte antigen (HLA) class I was detected in all three cell lines by flow cytometry using an anti-HLA monomorphic antibody, further serological analysis demonstrated HLA B38 loss in all three cell lines, HLA B7 downregulation in MJT5 (skin metastases) and B7 loss in MJT3 and MJT1 (brain metastases) compared with the HLA type of the patient's normal autologous lymphocytes. Interferon-gamma (IFNgamma) treatment increased the expression of HLA class I and transporters associated with antigen processing 1 (TAP1) in all three cell lines. De novo HLA class II molecule expression was observed after IFNgamma treatment in MJT3 and MJT5. Western blot and reverse transcription-polymerase chain reaction results revealed heterogeneity of melanoma-associated antigen (MAA) expression in the cell lines: MJT3 cells expressed higher levels of MAAs than the other two cell lines. In conclusion, this study has demonstrated that three metastatic lesions from a single patient can have differential expression of molecules involved in antigen processing (TAP1) and presentation (HLA I and II), but that expression of these molecules is modulated by IFNgamma to a similar degree in all cell lines. In contrast, the downregulation of expression of specific MAAs between the three cell lines was unaffected by the addition of IFNgamma.

Melanoma vaccines

Melanoma vaccines offer new hope to patients with metastatic melanoma, although convincing survival advantages have yet to be reported. This review outlines the progress made in this exciting field of research and looks ahead to the future.

Cancer immunotherapy: an embarrassment of riches?

There is clear evidence that certain forms of immunotherapy can be successful against certain cancers. However, it would appear that cancerous cells of various origin are exceptionally adept at subverting the immune response. Consequently, it is probable that the most efficacious therapy will be one in which multiple responses of the immune system are activated. There is currently an embarrassment of riches with regard to multiple vaccine strategies in the clinic, although no single method seems to hold the solution. Here, we draw together several of the humoral- and cellular-activating strategies currently under clinical investigation.

Cryopreservation of immature monocyte-derived dendritic cells results in enhanced cell maturation but reduced endocytic activity and efficiency of adenoviral transduction

To date, phase I/II dendritic cell (DC)-based cancer vaccine trials have required repeated venesection or leukapheresis to generate the DCs. Previous studies have suggested that DCs may be cryopreserved and revived for clinical use as sequential immunisations. We have developed a method of cryopreserving monocyte-derived DCs, reviving the cells with minimal loss, and have performed immunophenotypic and functional comparisons of freeze-thawed DCs with their fresh counterparts. We found that the freeze-thawing process itself is efficient in terms of DC recovery, results in semimaturation and reduced endocytic activity, but does not impair the capacity of the DCs to achieve full maturation. Revived cells also showed enhanced allostimulatory activity and antigen-specific responses. After freeze-thawing, DCs produced lower levels of IL-12 p40 and IL-12 p70 on maturation compared to fresh DCs with little change in concentration over 72 h. Genetic modification of DCs by adenoviral transduction was possible after cryopreservation albeit at a lower efficiency of gene transfer than with fresh cells. We conclude that cryopreservation of DCs for clinical immunotherapy is feasible. Modification of cells by pulsing or genetic transfer should take place prior to cryopreservation as the freeze-thawing process itself leads to increased maturation, reduction in endocytic activity but enhanced allostimulatory activity and antigen-specific responses.

Immunotherapeutic potential of whole tumour cells

Despite the identification of tumour antigens and their subsequent generation in subunit form for use as cancer vaccines, whole tumour cells remain a potent vehicle for generating anti-tumour immunity. This is because tumour cells express an array of target antigens for the immune system to react against, avoiding problems associated with major histocompatibility complex (MHC)-restricted epitope identification for individual patients. Furthermore, whole cells are relatively simple to propagate and are potentially efficient at contributing to the process of T cell priming. However, whole cells can also possess properties that allow for immune evasion, and so the question remains of how to enhance the immune response against tumour cells so that they are rejected. Scenarios where whole tumour cells may be utilised in immunotherapy include autologous tumour cell vaccines generated from resected primary tumour, allogeneic (MHC-disparate) cross-reactive tumour cell line vaccines, and immunotherapy of tumours in situ. Since tumour cells are considered poorly immunogenic, mainly because they express self-antigens in a non-stimulatory context, the environment of the tumour cells may have to be modified to become stimulatory by using immunological adjuvants. Recent studies have re-evaluated the relative roles of direct and cross-priming in generating anti-tumour immunity and have highlighted the need to circumvent immune evasion.

Study of immunological and virological parameters during thalidomide treatment of SIV-infected cynomolgus monkeys

The potential therapeutic utility of thalidomide (Thd), an effective inhibitor of tumor necrosis factor (TNF)-alpha in vitro, was investigated in cynomolgus monkeys (Macaca fascicularis) at 10 months after infection with simian immunodeficiency virus (SIV). Thd-treated macaques (n = 8) received an oral dose (10 mg) daily for 7 days, followed by a wash-out period of 5 weeks. A 2nd cycle of treatment was performed on the same animals at higher doses (20 mg Thd/day) for 14 days. The control monkeys (n = 7) received a placebo for the same period of time. In the present study, we show that Thd, in addition to inhibiting TNF-alpha production after in vitro mitogen stimulation of peripheral blood mononuclear cells (PBMCs), was able to restore the proliferative responses to SIV peptides in monkeys that were infected with SIV. Interestingly, we found that such effects are associated with an increased expression of CD28 cell surface receptors on CD4+ T-cells paralleled by a decrease on CD8+ T-cells. At the same time, significant reduction in either cell-associated viral load or plasma viral RNA was not observed among the SIV-infected monkeys during the two treatment cycles, when compared with the placebo group.

The conserved carboxy terminal region of HIV-1 gp120 is recognized by seronegative HIV-exposed people

OBJECTIVE

To screen HIV-positive, long-term exposed seronegative and low-risk individuals for the presence of antibodies against regions of HIV-1 gp120 that share some degree of homology with HLA.

METHODS

Sera were obtained from 63 HIV-1-infected subjects [52 Centers for Disease Control and Prevention (CDC) stage 2 and 11 stages 3/4], 32 HIV-exposed uninfected (HEU) subjects and from 24 low-risk HIV-1 seronegative individuals. They were tested by a peptide-based enzyme-linked immunosorbent assay (ELISA) for reactivity against peptides derived from the HIV-1 gp120 C-terminal region that contain regions of MHC sequence/structural similarity. Ten randomly selected sera from each group were also screened for anti-class I antibodies.

RESULTS

Thirty per cent of the long-term HIV-1-exposed seronegative individuals had antibodies against the conserved C-terminal region (C5) of HIV-1 gp120. However, sera from HEU individuals showed no reactivity against other peptides derived from the C2 region of gp120, also an HLA homologous region. Anti-C terminal gp120 antibodies were mainly of IgM subclass, although IgG-specific antibodies were also present. In addition, 70% of HEU individuals had antibodies to HLA class I molecules compared with 15% of HIV-positive patients (restricted to only those HIV-positive patients with anti C-terminal antibodies).

CONCLUSION

Our results suggest that antibody responses against the C-terminal region of HIV gp120 and HLA class I may represent markers of apparent natural protection against HIV-1 infection.

A lack of evidence for down-modulation of CD3 zeta expression in colorectal carcinoma and pregnancy using multiple detection methods

Loss of the T cell receptor-associated CD3 zeta chain has been proposed as a possible mechanism of the acquired immunosuppression in both tumour-bearing hosts, and in symptomatic patients with HIV infection. However, other reports suggest that the zeta-chain loss may in part be caused by protease activity of contaminating phagocytes ex vivo. Using flow cytometry and Western blot analysis on highly purified T cells, and ensuring adequate addition of protease inhibitors, we have studied the expression of CD3zeta on peripheral blood T cells from patients with colorectal carcinoma, and compared these with normal controls, and pregnant donors, as a further example of an immunocompromised state. Immunohistochemistry was performed on tumour sections from patients with colorectal carcinoma to measure CD3zeta expression in tumour infiltrating T cells, and compared with normal mucosa and tonsil. Using these three approaches, our data provide no evidence for downregulation of CD3zeta chain expression either in colorectal carcinoma or pregnancy and suggest that this explanation is unlikely to fully account for the reduced T cell function associated with these conditions in all patients.

The relevance of non-linear mathematics (chaos theory) to the treatment of cancer, the role of the immune response and the potential for vaccines

Non-linear mathematics or 'chaos' theory was first applied in the prediction of complex systems such as the weather. Chaotic systems exhibit not only apparently random unpredictability, but also a degree of determinism, in that randomness remains confined within specific parameters. Biological systems manifest many of the features of chaotic systems, including the inherent repetition of self, fractal structure, and the existence of strange attractors. In this article, the interaction between a tumour and the immune system is examined with regard to the capacity for immunotherapy to influence these two complex systems beneficially. It is postulated that judicious immunization may lead to profound changes in the stability of this interaction, in the favour of the immune system's ability to recognize tumour cells.

Evaluation of commercially available assays of neopterin and beta 2-microglobulin for the assessment of disease progression in FIV-infected cats

Serum or plasma samples from cats at different stages of feline immunodeficiency (FIV) infection and from uninfected cats were tested using immunoassays designed to detect human neopterin and beta 2-microglobulin (beta 2M). The results obtained from the anti-human neopterin assay did not correlate with infection status, time post-infection, fCD4 count or clinical picture. Feline samples gave negative results in the anti-human beta 2M assay. The assay kits used in this study are not suitable for the determination of the effect of FIV infection on immune activation markers in the cat.

Human T leukaemia virus type 1 (HTLV-1) specific T-helper cell response: clonal fluctuations and repertoire heterogeneity

The naive T-helper (Th) repertoire specific for HTLV-1 envelope (env) has been examined on antigen specific T-cell lines and clones from non-immune individuals. Clonal heterogeneity was determined by analysing the T-cell receptor (TCR) Vbeta gene usage and by sequencing the hypervariable regions of the TCR genes. Fluctuations in the V beta gene usage were determined by comparing the TCR Vbeta gene profiles of T-cell lines at different times. We found that a diverse repertoire for HTLV-1 env could be triggered in vitro. Diverse Vbeta genes were used by the same line tested at different times, suggesting that clonal composition of an antigen-specific T-cell line is not constant in vitro. Clones in fact may be up- and down-regulated and clonotypes undetectable at one time point can emerge upon subsequent restimulation. Therefore evaluation of the clonal composition of a T-cell line gives a snapshot of the dominant clones at the time of analysis, and does not tell the whole picture of the antigen-specific ensemble. Furthermore, by sequencing the TCR genes, we identified clones with identical Vbeta gene usage which differed in hypervariable regions (CDR3), indicating their derivation from independent precursors and contributing to overall clonal heterogeneity. If these data can be extended to HTLV-1-infected patients studied in vivo, the Th cell repertoire specific for HTLV-1 env may prove very heterogenous, with important implications for vaccine development.

New concepts in AIDS pathogenesis

The concept that HIV causes AIDS only by directly killing CD4 cells has been questioned by a number of investigators. There has been experimental support for a number of indirect mechanisms such as apoptosis, anergy, superantigen-induced cell proliferation and depletion, defective signaling, molecular mimicry, and autoimmunity. In this article we review the available evidence in support of these theories and suggest that in spite of their apparent differences, signaling by HIV through the T cell receptor could initiate the markedly different responses of activation, anergy, and apoptosis. However, the unifying mechanism as to how this is achieved remains unclear. It is likely that more than one of these mechanisms are involved in CD4 cell depletion during different phases of the disease. Understanding these mechanisms and their role in HIV pathogenesis would be important in new vaccine and therapeutic approaches.

Does the HIV envelope induce a chronic graft-versus-host-like disease?

Evidence is accumulating that susceptibility to disease following HIV infection is genetically restricted. In addition, activation of the immune response appears to play an important role in disease progression. Here, John Habeshaw and colleagues propose that HIV envelope glycoproteins mimic foreign MHC molecules and, in doing so, stimulate alloreactive lymphocytes. This activation may explain the marked clinical and immunological similarities between chronic GVHD and AIDS.

Localized conformational changes in the N-terminal domain of CD4 identified in competitive binding assay of monoclonal antibodies and HIV-1 envelope glycoprotein

The CD4 antigen is established as a major cellular receptor for the human immunodeficiency virus (HIV). Previous studies have suggested that certain anti-CD4 monoclonal antibodies (MAbs) can inhibit or enhance the binding of the viral envelope glycoprotein gp120 to CD4 by allosteric effects. In the study reported here, 17 anti-CD4 MAbs were tested for their ability to influence the binding of each other to recombinant soluble CD4 in a solid-phase radioimmunoassay. Marked enhancement of binding between specific pairs of MAbs was seen, as well as inhibition or lack of interaction. Enhancement was seen less often when CD4+ cells were used as the target antigen. Information on patterns of enhancement and inhibition permitted grouping of MAbs on the basis of epitope specificity, and this grouping was in agreement with published findings based on X-ray crystallographic studies. These results demonstrate connectivity between epitopes in the first domain of recombinant CD4 and suggest a high degree of flexibility of surface structure. These findings may be of physiological significance both in the normal function of CD4 and in the interaction of CD4 with HIV. The data have implications for research or therapeutic strategies based on recombinant CD4 or CD4 mutants and highlight the problems of interpreting experimental findings based on abrogation of MAb binding.

Sequential interleukin-2 and alpha interferon for renal cell carcinoma and melanoma

There is a theoretical basis for the synergy of interleukin-2 (IL-2) with other cytokines. We have investigated sequential treatment with IL-2 and alpha interferon. 1 of 22 patients with metastatic renal cell carcinoma had a partial response and one a minimal response to continuous infusion IL-2 but none of the 9 patients with melanoma responded. 16 of 17 patients with renal cell cancer, and 8 with melanoma, were then treated with alpha interferon. 2 patients with renal cell cancer responded to alpha interferon with sustained remissions of 30 and 40 months; both had responded to IL-2. The investigation of combination therapy with other cytokines is suggested, by these unusually long responses to alpha interferon.

HIV-1 proteinase is required for synthesis of pro-viral DNA

HIV-1 proteinase activity is thought to occur primarily post-integration by cleaving the viral Gag and Gag-Pol polyproteins. Its role in the pre-integration stages of viral replication, however, has not been studied in detail. Here we report that a synthetic peptide analogue, UK-88,947, which is a specific inhibitor of purified HIV-1 proteinase, inhibits the processing of the viral polyproteins in cultures of HIV-1 infected cells and prevents the formation of mature, infectious virions. Analysis of DNA from HIV-1 infected cells treated with UK-88,947 showed that viral DNA synthesis was inhibited when the compound was added to cultures one hour before infection. Similar results were obtained when AZT was used. Neither HIV-1 reverse transcriptase or the replication of FIV are inhibited by UK-88,947.

The naive repertoire of human T helper cells specific for gp120, the envelope glycoprotein of HIV

The envelope glycoprotein of HIV gp120 is a T cell Ag in experimental animals and in humans infected with HIV or deliberately immunized with gp120 in various forms. Inasmuch as T cell responses result from the interaction of Ag processed and presented by APC with the unprimed T cell repertoire, we have investigated the human T cell repertoire specific for gp120 in seronegative, normal individuals. T cell lines and clones specific for HIV gp120 were generated by repeated in vitro stimulation of peripheral blood T lymphocytes with gp120-pulsed APC, followed by IL-2 expansion. We observed that the T cell response to whole gp120 involved single restricted immunodominant epitopes in gp120 that differ between responding individuals. Focusing of the response to limited regions of gp120 when the whole Ag is used for priming suggests that one or more adjacent epitopes are immunodominant and mask responses to "immunorecessive" epitopes. We have been able to generate primary in vitro responses to recessive epitopes by stimulation in vitro with synthetic peptides of gp120. The results indicate that a much broader T repertoire can be detected when individual peptides are used for priming in vitro rather than gp120. This information has important implications for the development of vaccination protocols aimed at eliciting diverse immune responses to "immunorecessive" regions of envelope glycoprotein.