Tumor antigens and tumor vaccines: peptides as immunogens

Methionine oxidation selectively enhances T cell reactivity against a melanoma antigen

The impact of the peptide amino acids side-chain modifications on the immunological recognition has been scarcely explored. We investigate here the effect of methionine oxidation on the antigenicity of the melanoma immunodominant peptide 369-YMDGTMSQV-377 (YMD). Using CD8⁺ T cell activation assays, we found that the antigenicity of the sulfoxide form is higher when compared to the YMD peptide. This is consistent with free energy computations performed on HLA-A∗02:01/YMD/TCR complex showing that this is lowered upon oxidation, paired with a steep increase in order at atomic level. Oxidized YMD forms were identified at the melanoma cell surface by LC-MS/MS analysis. These results demonstrate that methionine oxidation in the antigenic peptides may generate altered peptide ligands with increased antigenicity, and that this oxidation may occur in vivo, opening up the possibility that high-affinity CD8⁺ T cells might be naturally primed in the course of melanoma progression, as a result of immunosurveillance.

The peptide woods are lovely, dark and deep: Hunting for novel cancer antigens

Harnessing the patient's immune system to control a tumor is a proven avenue for cancer therapy. T cell therapies as well as therapeutic vaccines, which target specific antigens of interest, are being explored as treatments in conjunction with immune checkpoint blockade. For these therapies, selecting the best suited antigens is crucial. Most of the focus has thus far been on neoantigens that arise from tumor-specific somatic mutations. Although there is clear evidence that T-cell responses against mutated neoantigens are protective, the large majority of these mutations are not immunogenic. In addition, most somatic mutations are unique to each individual patient and their targeting requires the development of individualized approaches. Therefore, novel antigen types are needed to broaden the scope of such treatments. We review high throughput approaches for discovering novel tumor antigens and some of the key challenges associated with their detection, and discuss considerations when selecting tumor antigens to target in the clinic.

Immunization with short peptide particles reveals a functional CD8+ T-cell neoepitope in a murine renal carcinoma model

BACKGROUND

Induction of CD8⁺ T cells that recognize immunogenic, mutated protein fragments in the context of major histocompatibility class I (MHC-I) is a pressing challenge for cancer vaccine development.

METHODS

Using the commonly used murine renal adenocarcinoma RENCA cancer model, MHC-I restricted neoepitopes are predicted following next-generation sequencing. Candidate neoepitopes are screened in mice using a potent cancer vaccine adjuvant system that converts short peptides into immunogenic nanoparticles. An identified functional neoepitope vaccine is then tested in various therapeutic experimental tumor settings.

RESULTS

Conversion of 20 short MHC-I restricted neoepitope candidates into immunogenic nanoparticles results in antitumor responses with multivalent vaccination. Only a single neoepitope candidate, Nesprin-2 L4492R (Nes2LR), induced functional responses but still did so when included within 20-plex or 60-plex particles. Immunization with the short Nes2LR neoepitope with the immunogenic particle-inducing vaccine adjuvant prevented tumor growth at doses multiple orders of magnitude less than with other vaccine adjuvants, which were ineffective. Nes2LR vaccination inhibited or eradicated disease in subcutaneous, experimental lung metastasis and orthotopic tumor models, synergizing with immune checkpoint blockade.

CONCLUSION

These findings establish the feasibility of using short, MHC-I-restricted neoepitopes for straightforward immunization with multivalent or validated neoepitopes to induce cytotoxic CD8⁺ T cells. Furthermore, the Nes2LR neoepitope could be useful for preclinical studies involving renal cell carcinoma immunotherapy.

CD4+ Th-APC with acquired peptide/MHC class I and II complexes stimulate type 1 helper CD4+ and central memory CD8+ T cell responses

T cell-T cell Ag presentation is increasingly attracting attention. We previously showed that the in vitro OVA-pulsed dendritic cell (DC(OVA))-activated CD4(+) Th cells acquired OVA peptide/MHC (pMHC) class I and costimulatory molecules such as CD54 and CD80 from DC(OVA) and acted as CD4(+) Th-APC capable of stimulating OVA-specific CD8(+) CTL responses. In this study, we further applied the OVA-specific TCR-transgenic OT I and OT II mice with deficiency of various cytokines or costimulatory molecule genes useful for studying the molecular mechanisms underlying in Th-APC's stimulatory effect. We demonstrated that DC(OVA)-stimulated OT II CD4(+) Th-APC also acquired costimulatory molecules such as CD40, OX40L, and 4-1BBL and the functional pMHC II complexes by DC(OVA) activation. CD4(+) Th-APC with acquired pMHC II and I were capable of stimulating CD4(+) Th1 and central memory CD8(+)44(+)CD62L(high)IL-7R(+) T cell responses leading to antitumor immunity against OVA-expressing mouse B16 melanoma. Their stimulatory effect on CD8(+) CTL responses and antitumor immunity is mediated by IL-2 secretion, CD40L, and CD80 signaling and is specifically targeted to CD8(+) T cells in vivo via acquired pMHC I. In addition, CD4(+) Th-APC expressing OVA-specific TCR, FasL, and perforin were able to kill DC(OVA) and neighboring Th-APC expressing endogenous and acquired pMHC II. Taken together, we show that CD4(+) Th-APC can modulate immune responses by stimulating CD4(+) Th1 and central memory CD8(+) T cell responses and eliminating DC(OVA) and neighboring Th-APC. Therefore, our findings may have great impacts in not only the antitumor immunity, but also the regulatory T cell-dependent immune tolerance in vivo.

Comparison Among Clark's, Breslow's, and TNM classifications for cutaneous head and neck malignant melanoma

This retrospective study was carried out to assess the prognostic value of three classification systems used for staging cutaneous head and neck malignant melanoma (CHNME). Fifty-three patients with histologically proven CHNME were analyzed. Thirty patients were never treated before admission, whereas 23 (43.4%) had a second radical resection of the primary tumor location, 9 (17%) had neck nodes, none had distant metastasis, and all had a minimum of 5 years of follow-up. Results show that T-stage is the most important clinical prognostic parameter, whereas Clark's and Breslow's classifications have lower impact in defining prognosis. Sites of primary tumor determines different clinical outcomes, but this does not reach statistically significant values. A second surgery on the primary tumor location is possible and is effective toward survival. No statistical differences were noted between the previously untreated and treated groups. Neck nodes have to be removed with neck dissection, and this regimen can improve the clinical outcome; however, only 40% of neck positive patients survive more than 5 years.

Novel exosome-targeted CD4+ T cell vaccine counteracting CD4+25+ regulatory T cell-mediated immune suppression and stimulating efficient central memory CD8+ CTL responses

T cell-to-T cell Ag presentation is increasingly attracting attention. In this study, we demonstrated that active CD4+ T (aT) cells with uptake of OVA-pulsed dendritic cell-derived exosome (EXO(OVA)) express exosomal peptide/MHC class I and costimulatory molecules. These EXO(OVA)-uptaken (targeted) CD4+ aT cells can stimulate CD8+ T cell proliferation and differentiation into central memory CD8+ CTLs and induce more efficient in vivo antitumor immunity and long-term CD8+ T cell memory responses than OVA-pulsed dendritic cells. They can also counteract CD4+25+ regulatory T cell-mediated suppression of in vitro CD8+ T cell proliferation and in vivo CD8+ CTL responses and antitumor immunity. We further elucidate that the EXO(OVA)-uptaken (targeted)CD4+ aT cell's stimulatory effect is mediated via its IL-2 secretion and acquired exosomal CD80 costimulation and is specifically delivered to CD8+ T cells in vivo via acquired exosomal peptide/MHC class I complexes. Therefore, EXO-targeted active CD4+ T cell vaccine may represent a novel and highly effective vaccine strategy for inducing immune responses against not only tumors, but also other infectious diseases.

The current status and future direction of percutaneous peptide immunization against melanoma

Dendritic cell (DC)-based tumor immunotherapy is widely known to elicit protective anti-tumor immune responses, although the safety and effectiveness have yet to be thoroughly explored. We reported that a disruption in the stratum corneum barrier resulted in enhanced permeability and alterations in the skin immune system in such a way that epidermal Langerhans cells (LCs) functioned as vigorous antigen presenters for T helper (Th) cells and cytotoxic T lymphocytes (CTLs). In both human and murine models, topical application of melanoma-associated antigen peptides onto stratum corneum barrier-disrupted skin, specifically induced tumoricidal immune responses in vivo and in vitro accompanying an increased expression of MHC and co-stimulatory molecules on LCs. In addition, for reasons of simplicity, safety and effectiveness, percutaneous peptide application has demonstrated a certain degree of feasibility in clinical approach in patients with melanoma. In the future, resolution of some of the outstanding issues concerning the selection of the most effective adjuvants in combination with barrier disruption and depletion of regulatory T (Treg) cell-mediated immune suppression would appear as essential to improve percutaneous melanoma immunotherapy.

CD4+ T cell acquisition of the bystander pMHC I colocalizing in the same immunological synapse comprising pMHC II and costimulatory CD40, CD54, CD80, OX40L, and 41BBL

We previously showed that CD4+ T cells acquired peptide/major histocompatibility complex (pMHC) I and costimulatory molecules by dendritic cell (DC) activation. However, the molecular mechanism for pMHC I acquisition is unclear. In this study, by using a panel of engineered DC2.4 cells or incubation of these cells with Con A-stimulated CD4+ T cells, we conducted capping and synapse formation assay and examined them by confocal fluorescence microscopy. We demonstrated that (i) CD54 and CD80 colocalized with pMHC I/II in the same lipid rafts, whereas CD40, OX40L, and 41BBL localized in the lipid rafts but separately from pMHC I/II, and (ii) MHC I/II colocalized with the costimulatory molecules in the same synapse formed between a DC and a CD4+ T cell, leading to expression of the acquired bystander pMHC I on CD4+ T cells via internalization/recycling pathway. These results provide some useful information in composition and dynamics of immunological synapses.

Nonspecific CD4(+) T cells with uptake of antigen-specific dendritic cell-released exosomes stimulate antigen-specific CD8(+) CTL responses and long-term T cell memory

Dendritic cell (DC) and DC-derived exosomes (EXO) have been used extensively for tumor vaccination. However, its therapeutic efficiency is limited to only production of prophylactic immunity against tumors. T cells can uptake DC-released EXO. However, the functional effect of transferred exosomal molecules on T cells is unclear. In this study, we demonstrated that OVA protein-pulsed DC-derived EXO (EXO(OVA)) can be taken up by Con A-stimulated, nonspecific CD4(+) T cells derived from wild-type C57BL/6 mice. The active EXO-uptaken CD4(+) T cells (aT(EXO)), expressing acquired exosomal MHC I/OVA I peptide (pMHC I) complexes and costimulatory CD40 and CD80 molecules, can act as APCs capable of stimulating OVA-specific CD8(+) T cell proliferation in vitro and in vivo and inducing efficient CD4(+) Th cell-independent CD8(+) CTL responses in vivo. The EXO(OVA)-uptaken CD4(+) aT(EXO) cell vaccine induces much more efficient CD8(+) T cell responses and immunity against challenge of OVA-transfected BL6-10 melanoma cells expressing OVA in wild-type C57BL/6 mice than EXO(OVA). The in vivo stimulatory effect of the CD4(+) aT(EXO) cell to CD8(+) T cell responses is mediated and targeted by its CD40 ligand signaling/acquired exosomal CD80 and pMHC I complexes, respectively. In addition, CD4(+) aT(EXO) vaccine stimulates a long-term, OVA-specific CD8(+) T cell memory. Therefore, the EXO(OVA)-uptaken CD4(+) T cells may represent a new, effective, EXO-based vaccine strategy in induction of immune responses against tumors and other infectious diseases.

In vitro expansion of Ag-specific T cells by HLA-A*0201-transfected K562 cells for immune monitoring

BACKGROUND

Development of a practical and sensitive assay for evaluating immune responses against cancer Ag has been a challenge for immune monitoring of patients. We have established a reproducible method using peptide-pulsed K562-A*0201 cells as APC to expand Ag-specific T cells in vitro. This method may be applied for monitoring T-cell responses in cancer immunotherapy clinical trials.

METHODS

Autologous PBMC from HLA-A*0201+ healthy donors and patients with melanoma were stimulated with peptide-pulsed K562-A*0201 cells under varying conditions. We investigated (1) different culture conditions, including the requirements for serum and cytokines for expansion of CD8+ T lymphocytes; (2) a range of peptide concentrations for Ag loading; (3) phenotypic characterization of responding T cells; and (4) APC:responder ratios and their effects on T-cell expansion. We validated these conditions by ELISPOT and intracellular cytokine staining (ICS) assays using peptides from influenza, Epslein-Barr Virus (EBV) and tyrosinase.

RESULTS

Conditions for optimal T-cell expansion using K562-A*0201 APC included input of 2 x 10(6) PBMC, a 10 microg/mL peptide concentration to pulse K562-A*0201 cells, a 1:30 APC:responder T-cell ratio and culture in 10% autologous plasma supplemented with IL-2 and IL-15. In these conditions, Ag-specific T cells expanded >100-fold over a 10-day culture period (peak at day 12).

DISCUSSION

This bulk culture method is simple and reliable for expanding human Ag-specific T cells using peptide-pulsed K562-A*0201 cells. This HLA-matched APC line can be adapted to other HLA haplotypes, and has advantages for monitoring clinical trials of immunotherapy with limited availability of autologous APC and PBMC from patients.

Mature dendritic cells pulsed with exosomes stimulate efficient cytotoxic T-lymphocyte responses and antitumour immunity

Exosomes (EXO) derived from dendritic cells (DC), which express major histocompatibility complex (MHC) and costimulatory molecules, have been used for antitumour vaccines. However, they are still less effective by showing only prophylatic immunity in animal models or very limited immune responses in clinical trials. In this study, we showed that ovalbumin (OVA) protein-pulsed DC (DC(OVA))-derived EXO (EXO(OVA)) displayed MHC class I-OVA I peptide (pMHC I) complexes, CD11c, CD40, CD80, CCR7, DEC205, Toll-like receptor 4 (TLR4), TLR9, MyD88 and DC-SIGN molecules, but at a lower level than DC(OVA). EXO(OVA) can be taken up by DC through LFA-1/CD54 and C-type lectin/mannose (glucosamine)-rich C-type lectin receptor (CLR) interactions. Mature DC pulsed with EXO(OVA), which were referred to as mDC(EXO), expressed a higher level of pMHC I, MHC II, and costimulatory CD40, CD54 and CD80 than DC(OVA). The mDC(EXO) could more strongly stimulate OVA-specific CD8(+) T-cell proliferation in vitro and in vivo, and more efficiently induce OVA-specific cytotoxic T-lymphocyte responses, antitumour immunity and CD8(+) T-cell memory in vivo than EXO(OVA) and DC(OVA). In addition, mDC(EXO) could also more efficiently eradicate established tumours. Therefore, mature DC pulsed with EXO may represent a new, highly effective DC-based vaccine for the induction of antitumour immunity.

Intradermal Vaccination of Dendritic Cell–Derived Exosomes Is Superior to a Subcutaneous One in the Induction of Antitumor Immunity

Because dendritic cell (DC)-derived exosomes (EXO) harbor many important DC molecules involved in inducing immune responses, EXO-based vaccines have been extensively used to induce antitumor immunity in different animal tumor models. However, it is not clear which route of EXO administration can induce more efficient antitumor immune responses. In this study, we compared the antitumor immunity derived from EXO vaccine by way of the two common administration routes, the subcutaneous (s.c.) and the intradermal (i.d.) administrations. Our data showed that the i.d. EXO administration resulted in more EXO-absorbed DC migrating into the T-cell areas of draining lymph nodes than the s.c. administration. Interestingly, the i.d. EXO administration also resulted in an enhanced ovalbumin (OVA)-specific CD8(+) T-cell proliferation and CD8(+) CTL effector responses in vivo, compared to the s.c. administration. Similarly, compared to the s.c. vaccination, the i.d. vaccination induced stronger antitumor immunity in the animal tumor model. Therefore, the i.d. EXO vaccination is superior to the s.c. one and should be considered when EXO-based vaccine is designed.

A New Dynamic Model of CD8+T Effector Cell Responses via CD4+T Helper-Antigen-Presenting Cells

A long-standing paradox in cellular immunology has been the conditional requirement for CD4(+) Th cells in priming of CD8(+) CTL responses. We propose a new dynamic model of CD4(+) Th cells in priming of Th-dependent CD8(+) CTL responses. We demonstrate that OT II CD4(+) T cells activated by OVA-pulsed dendritic cells (DC(OVA)) are Th1 phenotype. They acquire the immune synapse-composed MHC II/OVAII peptide complexes and costimulatory molecules (CD54 and CD80) as well as the bystander MHC class I/OVAI peptide complexes from the DC(OVA) by DC(OVA) stimulation and thus also the potential to act themselves as APCs. These CD4(+) Th-APCs stimulate naive OT I CD8(+) T cell proliferation through signal 1 (MHC I/OVAI/TCR) and signal 2 (e.g., CD54/LFA-1 and CD80/CD28) interactions and IL-2 help. In vivo, they stimulate CD8(+) T cell proliferation and differentiation into CTLs and induce effective OVA-specific antitumor immunity. Taken together, this study demonstrates that CD4(+) Th cells carrying acquired DC Ag-presenting machinery can, by themselves, efficiently stimulate CTL responses. These results have substantial implications for research in antitumor and other aspects of immunity.

Regulated folding of tyrosinase in the endoplasmic reticulum demonstrates that misfolded full-length proteins are efficient substrates for class I processing and presentation

Short-lived protein translation products have been proposed to be the principal substrates that enter the class I MHC processing and presentation pathway. However, the biochemical nature of these substrates is poorly defined. Whether the major processing substrates are misfolded full-length proteins, or alternatively, aberrantly initiated or truncated polypeptides still remains to be addressed. To examine this, we used melanoma in which one-third of wild-type tyrosinase molecules were correctly folded and localized beyond the Golgi, while the remainder were present in the endoplasmic reticulum in an unfolded/misfolded state. Increasing the efficiency of tyrosinase folding using chemical chaperones led to a reduction in the level of substrate available to the proteasome and decreased the expression of a tyrosinase-derived epitope. Conversely, in transfectants expressing tyrosinase mutants that are completely misfolded, both proteasome substrate and epitope presentation were significantly enhanced. Proteasome substrate availability was a consequence of misfolding and not simply due to retention in the endoplasmic reticulum. Thus, the extent of folding/misfolding of a full-length protein is an important determinant of the level of epitope presentation.

Generation of a human leukocyte antigen-A24–restricted antitumor cell with the use of SART-1 peptide and dendritic cells in patients with malignant brain tumors

Dendritic cells (DCs) can be the principal initiators of antigen-specific immune responses. In this study, we attempted to generate cytotoxic T-lymphocytes (CTLs) using DCs pulsed with SART-1(254) peptide. Peripheral-blood mononuclear cells (PBMCs) and tumor-infiltrating mononuclear cells (TIMCs) were obtained from 11 patients with brain tumors expressing human leukocyte antigen (HLA)-A24. After stimulation with SART-1(254) peptide, CTLs showing over 15% were observed in one of 4 patients with gliomas and in 4 of 7 patients with metastatic brain tumors. Furthermore, exposure to DCs pulsed with SART-1(254) peptide increased the killing activity of these CTLs by 28.7% and 37.5%, respectively. We conclude that DCs pulsed with SART-1(254) peptide are effective in generating HLA-A24-restricted antitumor cells.

Vaccine therapy for cutaneous T-cell lymphoma

We demonstrated that percutaneous peptide immunization by way of skin with impaired barrier function is a simple and noninvasive strategy to generate effective immune responses against tumors. This therapeutic strategy seems to be beneficial for the treatment of skin-associated malignancies, including CTCL, because specific CTLs are considered to be well-induced in lymph nodes that neighbor barrier-disrupted skin (Fig. 3). There remain unsolved issues concerning (1) the ability of cytokines and growth factors to enhance efficacy of this therapy and (2) the time schedule of clinical trials. It was recently shown that application of antigenic protein or its coding DNA to skin with increased permeability yields antigen-specific antibody responses. Because the skin represents an easily accessible site for immunization and vaccination, percutaneous immunization using corneum barrier-disrupted skin is an alternative to injection of CTL-inducing molecules and can readily be exploited for cancer treatment in humans. The effective induction of CTLs suggests that the method that uses barrier-disrupted skin can potentially be applied to treatments of virus and helminth infections with the use of certain antigenic peptides.

Clinical and Immunologic Results of a Randomized Phase II Trial of Vaccination Using Four Melanoma Peptides Either Administered in Granulocyte-Macrophage Colony-Stimulating Factor in Adjuvant or Pulsed on Dendritic Cells

Purpose: To determine clinical and immunologic responses to a multipeptide melanoma vaccine regimen, a randomized phase II trial was performed.

Patients and Methods: Twenty-six patients with advanced melanoma were randomly assigned to vaccination with a mixture of four gp100 and tyrosinase peptides restricted by HLA-A1, HLA-A2, and HLA-A3, plus a tetanus helper peptide, either in an emulsion with granulocyte-macrophage colony-stimulating factor (GM-CSF) and Montanide ISA-51 adjuvant (Seppic Inc, Fairfield, NJ), or pulsed on monocyte-derived dendritic cells (DCs). Systemic low-dose interleukin-2 (Chiron, Emeryville, CA) was given to both groups. T-lymphocyte responses were assessed, by interferon gamma ELIspot assay (Chiron, Emeryville, CA), in peripheral-blood lymphocytes (PBLs) and in a lymph node draining a vaccine site (sentinel immunized node [SIN]).

Results: In patients vaccinated with GM-CSF in adjuvant, T-cell responses to melanoma peptides were observed in 42% of PBLs and 80% of SINs, but in patients vaccinated with DCs, they were observed in only 11% and 13%, respectively. The overall immune response was greater in the GM-CSF arm (P < .02). Vitiligo developed in two of 13 patients in the GM-CSF arm but in no patients in the DC arm. Helper T-cell responses to the tetanus peptide were detected in PBLs after vaccination and correlated with T-cell reactivity to the melanoma peptides. Objective clinical responses were observed in two patients in the GM-CSF arm and one patient in the DC arm. Stable disease was observed in two patients in the GM-CSF arm and one patient in the DC arm.

Conclusion: The high frequency of cytotoxic T-lymphocyte responses and the occurrence of clinical tumor regressions support continued investigation of multipeptide vaccines administered with GM-CSF in adjuvant.

Antitumor immunopreventive and immunotherapeutic effect in mice induced by hybrid vaccine of dendritic cells and hepatocarcinoma in vivo

AIM: To develop atumor vaccine by fusion of H22 hepatocarcinoma cells and DC, and to study its protective and therapeutical effect against H22 cell.

METHODS: H22-DC vaccine was produced by PEG fusion of H22 and DC induced by cytokine released from splenic mononuclear cells, sorted by CD11c magnetic microbead marker. It was injected through the tail vein of the mice and the H₂₂-DC oncogenesis was detected in the liver, spleen and lung. In order to study the therapeutical and protective effect of H₂₂-DC against tumor H₂₂, two groups were divided: immune group and therapeutic group. Immune group was further divided into P, D, HD and H subgroups, immunized by PBS, DC, H₂₂-DC and inactivated H₂₂, respectively, and attacked by H₂₂ cell. The tumor size, tumor weight, mice survival time and tumor latent period were recorded and statistically analyzed; Therapeutical group was divided into three subgroups of P, D and HD, and attacked by H₂₂, then treated with PBS, DC, and H₂₂-DC, respectively. Pathology and flow cytometry were also applied to study the mechanism how the H₂₂-DC vaccine attacked on the H₂₂ cell.

RESULTS: 1. No oncogenesis was found in spleen, lung and liver after H22-DC injection. 2. Hybrid vaccine immunized mice had strongest CTL activity. 3. In the immune group, latent period was longer in HD subgroup than that in P, H and D subgroup; and tumor size and weight were smaller in HD subgroup than that in P, H and D subgroup. 4. In therapeutic group, tumor size was smaller in HD subgroup than that in P, D subgroup.

CONCLUSION: 1. H22-DC tumor vaccine is safe without oncogenesis in vivo. 2. Hybrid vaccine can stimulate potent specific CTL activity against H22. 3. H22-DC vaccine has distinctive prophylatic effect on tumor H22 and can inhibit the tumor growth.

Antimelanoma activity of CTL generated from peripheral blood mononuclear cells after stimulation with autologous dendritic cells pulsed with melanoma gp100 peptide G209-2M is correlated to TCR avidity

Anchor residue-modified peptides derived from tumor-associated Ag have demonstrated success in engendering immune responses in clinical studies. However, tumor regression does not always correlate with immune responses. One hypothesis to explain this is that CTL resulting from such immunization approaches are variable in antitumor potency. In the present study, we evaluated this hypothesis by characterizing the activity of tumor-associated Ag-specific CTL. We chose an anchor residue-modified peptide from gp100, G209-2M, and used peptide-pulsed dendritic cells to generate CTL from PBMC of HLA-A2(+) normal donors. The specificities and avidities of the resulting CTL were evaluated. The results demonstrate that CTL generated by G209-2M can be classified into three categories: G209-2M-specific CTL which are cytotoxic only to G209-2M-pulsed targets; peptide-specific CTL which recognize both G209 and G209-2M peptides but not melanomas; and melanoma-reactive CTL which recognize peptide-pulsed targets as well as HLA-A2(+)gp100(+) melanomas. CTL that kill only peptide-pulsed targets require a higher peptide concentration to mediate target lysis, whereas CTL that lyse melanomas need a lower peptide concentration. Increasing peptide density on melanomas by loading exogenous G209 peptide enhances their sensitivity to peptide-specific CTL. High avidity CTL clones also demonstrate potent antimelanoma activity in melanoma model in nude mice. Injection of G209 peptide around transplanted tumors significantly enhances the antitumor activity of low avidity CTL. These results suggest that peptide stimulation causes expansion of T cell populations with a range of avidities. Successful immunotherapy may require selective expansion of the higher-avidity CTL and intratumor injection of the peptide may enhance the effect of peptide vaccines.

Mobilization of dendritic cells from patients with breast cancer into peripheral blood stem cell leukapheresis samples using Flt-3-Ligand and G-CSF or GM-CSF

Treatment with myeloablative chemotherapy and autologous peripheral blood stem cell (PBSC) transplantation followed by vaccination with autologous dendritic cells (DCs) treated with tumor antigens is a promising therapeutic strategy for several types of cancer. Obtaining sufficient numbers of both PBSCs and DCs is central to this approach. Previously, it has been shown that administration of Flt-3-Ligand (FL) combined with either G-CSF or GM-CSF mobilizes large numbers of PBSCs in patients with cancer. In the current study, we sought to determine whether these same cytokines could simultaneously mobilize DCs into the PBSC leukapheresis collection. DCs were analysed in PBSC leukapheresis samples obtained from five patients with high-risk breast cancer who received G-CSF alone as priming prior to leukapheresis, four patients who received FL+G-CSF and five patients who received FL+GM-CSF. DCs were defined as cells with a lin(dim/-) HLA-DR+ CD11c+ phenotype. The proportions of DCs in the FL+G-CSF and FL+GM-CSF samples were significantly higher than in pre-mobilization peripheral blood and G-CSF leukapheresis samples. The mean yield of DCs/kg in the FL+GM-CSF samples was also significantly higher than the mean yield of DCs in the G-CSF samples. The FL+G-CSF and FL+GM-CSF mobilized DCs were immature by morphologic and phenotypic criteria but stimulated allogeneic T-cells at levels similar to DCs generated in culture from PBMCs. Overnight culture?of the immature DCs obtained from patients receiving either FL+G-CSF or FL+GM-CSF in TNF-alpha?resulted in the generation of mature DCs. In summary, administration of FL in combination with GM-CSF and G-CSF to patients with breast cancer can mobilize large numbers of immature DCs into PBSC leukapheresis collections.

Vaccination for melanoma

Our knowledge of the immune system has grown tremendously in the 50 years since Coley used bacteria in an attempt to create a vaccine for cancer. The strategy for cancer vaccines has developed in that time as well. Both clinical and laboratory evidence suggests that melanoma is the more immunogenic of solid tumors. If treated early, melanoma can be controlled with surgery, but many patients continue to die from it. With our increased understanding of the immune system's interaction with melanoma, many clinical trials of melanoma vaccines are now underway. Vaccines designed to treat metastatic melanoma have shown some evidence of clinical effectiveness. This article outlines the current status of melanoma vaccination.

Reduction in serum IL-6 after vacination of breast cancer patients with tumour-associated antigens is related to estrogen receptor status

Elevated serum IL-6 concentrations have been associated with poor prognosis in a variety of cancers, and decreases in serum IL-6 concentrations have been reported after chemotherapy. We have demonstrated that serum IL-6 concentrations are elevated in breast cancer patients [normal women 0.7 +/- 2.5 pg/ml (n=36), breast cancer patients 38.3 +/- 138.7 pg/ml (n = 111)]. After vaccination of breast cancer patients with a combination of tumour-associated antigens and biological adjuvants (IL-2 and GM-CSF), the concentration of IL-6 decreased significantly (P<0.05) to 8.1 +/- 14.6 pg/ml (n=85). Other studies have shown that oestrogen suppresses IL-6 production in oestrogen receptor positive breast cancer cells. We have demonstrated that the decrease in IL-6 associated with vaccination is related to the oestrogen receptor status of the tumours from breast cancer patients, as a decrease in IL-6 from 124.0 +/- 267.5 pg/ml (n=26) to 6.2 +/- 11.0 pg/ml (n=34) only occurs in patients with oestrogen receptor negative tumours. The IL-6 concentration in breast cancer patients with oestrogen receptor positive tumours remained unchanged (9.5 pg/ml before vaccination, and 9.3 pg/ml after vaccination). These results suggest that postmenopausal women with oestrogen receptor negative breast cancers, who do not respond well to either hormonal therapy with tamoxifen or adjuvant chemotherapy, may have a significant response to vaccination with autologous tumour-associated antigens.

Melanoma vaccines

Remarkable advances in tumor vaccination have been made since Coley first deliberately infected cancer patients with both live and heat-killed bacteria. Melanoma is the most immunogenic solid tumor and, as such, has served as the major model for tumor vaccine investigation in both the laboratory and the clinic. Many advances in the field of melanoma vaccination have been based on an improved understanding of the cellular interaction required to induce a specific antitumor immune response. As a result of this new knowledge, many clinical trials of melanoma vaccines are now under way, and vaccines for metastatic melanoma have shown evidence of clinical effectiveness. This paper outlines the current status of melanoma vaccination.

Increasing the frequency of T-cell precursors specific for a cryptic epitope of hen-egg lysozyme converts it to an immunodominant epitope

Efforts to understand the mechanisms that govern how immunodominant T-cell epitopes are selected from protein antigens have focused mostly on differences in the efficiency of processing and presentation of peptide/major histocompatibility complex (MHC) complexes by antigen-presenting cells, while little attention has been directed at the role of the T-cell repertoire. In this report, the influence of the T-cell repertoire on immunodominance was investigated using transgenic mice that express the beta chain from a T-cell receptor specific for a cryptic Ek restricted epitope of hen-egg lysozyme, HEL85-96. In these mice, the frequency of HEL85-96-specific T-cell precursors is increased 10-20-fold over non-transgenic mice. Transgenic mice respond as well as non-transgenic controls to intact HEL, even though they respond poorly or not at all to a variety of other antigens, including the dominant H-2k restricted epitopes of HEL. Following immunization with native HEL, the only HEL peptide that could recall a response in vitro in the transgenic mice was HEL85-96. Therefore, this normally cryptic epitope is the sole immunodominant epitope in the transgenic mice, and this alteration in immune response is due solely to an increase in the frequency of specific T-cell precursors. An analysis of four additional H-2k restricted cryptic epitopes of HEL suggests that three are similarly limited by T-cell frequency, and that only one is consistent with a defect in efficient antigen presentation. This indicates that there are at least two different types of cryptic epitopes, one in which crypticity is caused by inefficient processing or presentation, and another in which the frequency of specific T-cell progenitors is limiting.

Overview of viruses, cancer, and vaccines in concept and in reality

Cancer is a consequence of malfunction of the replicative cell cycle caused by acquisition of independence from proliferative and restrictive controls in the process. Such alteration may be driven by unrepaired mutations in proto-oncogenes and anti-oncogenes or by genetic insults of environmental, infectious, or spontaneous origin. The consequence of mutations may be reflected at any of a number of locations in the transductive pathways from receptor to nucleus which upset normal homeostatic balance between the opposing forces for promotion or restraint of cell proliferation. About 15% of human cancers are caused primarily by viruses that bring about aberrations in gene structure and function or that express proteins that bind to cell regulatory proteins. The means for achieving immunoprophylaxis of viral cancers, such as hepatitis B or Marek's disease, are based on prior specific perturbation of the immune system, causing it to respond rapidly and effectively in preventing infection on subsequent contact with the corresponding agent. Existing cancers of viral origin and those of nonviral causation come together in attempted immunotherapy. Cure is far more difficult to achieve than prevention and relies on the principle that tumor cells can display abnormal markers on the cell surface that are capable of being detected and engaged by an effective immune response. Efforts to prevent and cure cancer of viral, spontaneous, or environmental origin are a worthy pursuit and must take account of the most advanced information relating to the chemistry of the cell cycle and to the function of the immune system.

Complete spontaneous regression of pulmonary metastatic melanoma

BACKGROUND

Complete spontaneous regression of melanoma metastatic to the lungs is a rare event.

OBJECTIVE

To report a case of biopsy-proven melanoma metastatic to the lung with complete spontaneous regression.

METHODS

Multidisciplinary case report.

RESULTS

A 35-year-old white female was diagnosed with metastatic melanoma to the lung. A pleural biopsy confirmed the diagnosis. Partial spontaneous regression was noted by a staging computed tomography scan prior to enrollment in an investigational protocol. Complete spontaneous regression occurred over 5 months without any form of conventional or alternative therapy, and the patient remains disease-free 3 years after diagnosis.

CONCLUSIONS

Our case represents the seventh case of complete spontaneous regression of melanoma metastatic to the lung, and the only case with histologic confirmation of both the primary and pulmonary metastatic lesions. The patient was pregnant twice between the time of her initial diagnosis of primary melanoma and pulmonary metastatic disease.

Human Melanoma-Reactive CD4+ and CD8+ CTL Clones Resist Fas Ligand-Induced Apoptosis and Use Fas/Fas Ligand-Independent Mechanisms for Tumor Killing

Tumor cells have been shown recently to escape immune recognition by developing resistance to Fas-mediated apoptosis and acquiring expression of Fas ligand (FasL) molecule that they may use for eliminating activated Fas+ lymphocytes. In this study, we report that tumor-specific T lymphocytes isolated from tumor lesions by repeated in vitro TCR stimulation with relevant Ags (mostly represented by normal self proteins, such as MART-1/Melan A and gp100) can develop strategies for overcoming these escape mechanisms. Melanoma cells (and normal melanocytes) express heterogeneous levels of Fas molecule, but they result homogeneously resistant to Fas-induced apoptosis. However, CD4+ and CD8+ CTL clones kill melanoma cells through Fas/FasL-independent, granule-dependent lytic pathway. In these lymphocytes, Ag/MHC complex interaction with TCR does not lead to functional involvement of FasL, triggered, on the contrary, by T cell activation with nonspecific stimuli such as PMA/ionomycin. Additionally, melanoma cells express significant levels of FasL (detectable on the cell surface only after treatment with metalloprotease inhibitors), although to a lesser extent than professional immune cells such as Th1 clones. Nevertheless, antimelanoma CTL clones resist apoptosis mediated by FasL either in soluble form or expressed by Th1 lymphocytes or FasL+ melanoma cells. These results demonstrate that CD4+ and CD8+ antimelanoma T cell clones can be protected against Fas-dependent apoptosis, and thus be useful reagents of immunotherapeutic strategies aimed to potentiate tumor-specific T cell responses.

Bacterial lipopolysaccharide contamination of commercial collagen preparations may mediate dendritic cell maturation in culture

Dendritic cells (DC) are potent antigen presenting cells, which are responsible for the initiation of naive T and T-dependent immune responses. The present studies were based upon recent reports that commercial collagen I preparations induce the maturation of human DC in vitro. We show that human blood monocyte-derived (GM-CSF and IL-4 cultured) DC pulsed on collagen I-coated plates undergo a dose-dependent increase in stimulatory capacity in oxidative mitogenesis assays. This is accompanied by the upregulation of costimulatory molecules (CD40, CD80, CD86), CD25, ICAM-1 and the DC-specific marker CD83. The maturation effect is more potent than TNF-alpha, which is a known mediator of DC function. However, bacterial lipopolysaccharide (LPS), a powerful inducer of DC maturation, was found to be present at very high levels in one commercial collagen solution that was tested. The effect of LPS upon DC maturation was similar to culture with collagen. Furthermore, a different collagen I preparation with low levels of LPS contamination was less effective at inducing DC maturation, while spiking the collagen solution with LPS prior to plastic coating equalised these effects. Finally, human monocyte-derived DC were found not to express typical collagen receptors VLA-1, 2 and 3. We therefore propose that LPS contamination may at least partially explain reported collagen I induced DC maturation.

Advances in melanoma therapy

This review discusses several advances in melanoma therapy that have recently occurred or are presently in a developmental stage. We discuss the history and present dogma regarding assessment of the regional lymph nodes and adjuvant therapy for melanoma. Of special interest is radiolymphatic sentinel node mapping of the lymph nodes and adjuvant interferon alfa-2b for thick primary lesions and stage III disease. We also discuss several evolving novel and innovative genetic immunotherapy approaches for patients with stage IV disease.

Report of immune monitoring of prostate cancer patients undergoing T-cell therapy using dendritic cells pulsed with HLA-A2-specific peptides from prostate-specific membrane antigen (PSMA)

BACKGROUND

In this paper we describe our program for the immune monitoring of phase II participants given dendritic cell (DC)/prostate-specific membrane antigen (PSMA)-based immunotherapy, and we also present some initial findings.

METHODS

Phase II subjects received six administrations of autologous dendritic cells exogenously pulsed with two peptides derived from PSMA. Prior to the initial infusion, and following each treatment, peripheral blood mononuclear cells (PBMC) were collected for the generation of dendritic cells as well as for comprehensive immune monitoring.

RESULTS

Thus far, an increase in PSMA-peptide-specific as well as overall cellular reactivity has been observed in several patients receiving DC plus PSM-P1 and -P2, as measured by delayed-type hypersensitivity (DTH) test and enzyme-linked immunosorbant assay (ELISA).

CONCLUSIONS

Our initial observations using an ELISA and DTH test indicate that we are enhancing cellular immunity in prostate cancer patients following infusion with DC plus PSMA-derived peptides. Several methods are underway to comprehensively monitor both cell-mediated and humoral immune responsiveness, including: determining anti-PSMA serum antibody titers, testing immunogen-restricted responder-cell proliferation and cytotoxicity, assessing aberrations in signal transduction, antigen processing, and presentation, and measuring soluble factors that may promote tumor outgrowth.

Biologic therapy of melanoma with cytokines and lymphocytes

Melanoma has a somewhat unpredictable behavior, and spontaneous regressions do occasionally occur. Many have surmised that these are the result of immunologic attack by the host. Immunologic treatment has been more successful for melanoma than for most other neoplasms, even with relatively crude therapies, such as bacterial products. With the availability of recombinant cytokines, immunotherapy for melanoma has entered a new era. Interleukin-2 (IL-2), which acts entirely through immunologic mechanisms, has been tested extensively, either alone, in combination with other cytokines, or with adoptive cellular therapy. Alone, it has only modest antitumor activity, even at high doses. Its utility may be greater when combined with immunocompetent cells, especially tumor-sensitized T lymphocytes, in adoptive immunotherapy. On the other hand, nonspecific lymphokine-activated killer (LAK) cells do not appear to add significantly to the efficacy of IL-2 alone. Interferon-alpha (IFN-alpha) [corrected] also has had fairly limited activity in the advanced disease setting, but, on the basis of a recently completed randomized trial, has arguably become the "standard of care" in the adjuvant setting for patients with high-risk melanoma, particularly node-positive patients. A number of regimens combining IL-2, IFN-alpha, and chemotherapeutic agents have yielded striking response rates in small trials and await confirmation in larger studies. With better delineation of the host immune response and definition of relevant tumor antigens, we can look forward to exciting results with combinations of vaccines, cytokines, and adoptive cellular approaches, particularly in patients with micrometastatic disease.