Identification of a New Shared HLA-A2.1 Restricted Epitope From the Melanoma Antigen Tyrosinase:

Anti-BCMA chimeric antigen receptors with fully human heavy-chain-only antigen recognition domains

Chimeric antigen receptor (CAR)-expressing T cells targeting B-cell maturation antigen (BCMA) have activity against multiple myeloma, but improvements in anti-BCMA CARs are needed. We demonstrated recipient anti-CAR T-cell responses against a murine single-chain variable fragment (scFv) used clinically in anti-BCMA CARs. To bypass potential anti-CAR immunogenicity and to reduce CAR binding domain size, here we designed CARs with antigen-recognition domains consisting of only a fully human heavy-chain variable domain without a light-chain domain. A CAR designated FHVH33-CD8BBZ contains a fully human heavy-chain variable domain (FHVH) plus 4-1BB and CD3ζ domains. T cells expressing FHVH33-CD8BBZ exhibit similar cytokine release, degranulation, and mouse tumor eradication as a CAR that is identical except for substitution of a scFv for FHVH33. Inclusion of 4-1BB is critical for reducing activation-induced cell death and promoting survival of T cells expressing FHVH33-containing CARs. Our results indicate that heavy-chain-only anti-BCMA CARs are suitable for evaluation in a clinical trial.

Secreted heat shock protein gp96-Ig: next-generation vaccines for cancer and infectious diseases

Over the past decade, our laboratory has developed a secreted heat shock protein (HSP), chaperone gp96, cell-based vaccine that generates effective anti-tumor and anti-infectious immunity in vivo. Gp96-peptide complexes were identified as an extremely efficient stimulator of MHC I-mediated antigen cross-presentation, generating CD8 cytotoxic T-lymphocyte responses detectable in blood, spleen, gut and reproductive tract to femto-molar concentrations of antigen. These studies provided the first evidence that cell-based gp96-Ig-secreting vaccines may serve as a potent modality to induce both systemic and mucosal immunity. This approach takes advantage of the combined adjuvant and antigen delivery capacity of gp96 for the generation of cytotoxic immunity against a wide range of antigens in both anti-vial and anti-cancer vaccination. Here, we review the vaccine design that utilizes the unique property/ability of endoplasmic HSP gp96 to bind antigenic peptides and deliver them to antigen-presenting cells.

A new tyrosinase epitope recognized in the HLA-B*4002 context by CTL from melanoma patients

Melanoma reactive CTL were obtained by stimulating PBL from a melanoma patient in remission since 1994 following adjuvant TIL immunotherapy, with the autologous melanoma cell line. They were cloned by limiting dilution. One CTL clone recognized melanoma cell lines expressing tyrosinase and the B*4002 molecule, either spontaneously or upon transfection. We demonstrated that this clone recognizes the tyrosinase-derived nonapeptide 316-324 (ADVEFCLSL) and the overlapping decapeptide 315-324 (SADVEFCLSL). We derived two distinct additional specific CTL clones from this same patient that were also reactive against B*4002 melanoma cell lines, suggesting a relative diversity of this specific repertoire in this patient. Stimulating PBMC derived from four additional B*4002 melanoma patients with the tyrosinase 316-324 nonapeptide induced the growth of specific cells for two of the patients, demonstrating the immunogenicity of this new epitope. Our data show that this nonapeptide is a new tool that could be used to generate melanoma-specific T cells for adoptive immunotherapy or serve as a peptide vaccine for HLA-B*4002 melanoma patients.

Evaluation of prime/boost regimens using recombinant poxvirus/tyrosinase vaccines for the treatment of patients with metastatic melanoma

PURPOSE

Two clinical trials were conducted to evaluate the clinical efficacy and immunologic impact of vaccination against the tyrosinase protein plus systemic interleukin 2 (IL-2) administration in patients with advanced metastatic melanoma.

EXPERIMENTAL DESIGN

Full-length tyrosinase was employed as an immunogen to induce diverse immunologic responses against a commonly expressed melanoma antigen. Heterologous prime/boost vaccination with recombinant vaccinia and fowlpox vectors encoding tyrosinase was first explored in a randomized three-arm phase II trial, in which vaccines were administered alone or concurrently with low-dose or high-dose IL-2. In a subsequent single cohort phase II trial, all patients received the same vaccines and high-dose IL-2 sequentially rather than concurrently.

RESULTS

Among a total of 64 patients treated on these trials, 8 objective partial responses (12.5%) were observed, all in patients receiving high-dose IL-2. Additional patients showed evidence of lesional regression (mixed tumor response) or overall regression that did not achieve partial response status (minor response). In vitro evidence of enhanced immunity against tyrosinase following protocol treatments was documented in 3 of 49 (6%) patients tested serologically, 3 of 23 (13%) patients tested for T-cell recognition of individual tyrosinase peptides, and 4 of 16 (25%) patients tested for T-cell recognition of full-length tyrosinase protein with real-time reverse transcription-PCR techniques.

CONCLUSIONS

Whereas prime/boost immunization with recombinant vaccinia and fowlpox viruses enhanced antityrosinase immunity in some patients with metastatic melanoma, it was ineffective alone in mediating clinical benefit, and in combination with IL-2 did not mediate clinical benefit significantly different from that expected from treatment with IL-2 alone.

Immunization of patients with the hTERT:540-548 peptide induces peptide-reactive T lymphocytes that do not recognize tumors endogenously expressing telomerase

PURPOSE

Telomerase is an attractive target antigen for cancer immunotherapies because it is expressed in >85% of human tumors but is rarely found in normal tissues. A HLA-A*0201-restricted T-cell epitope was previously identified within telomerase reverse transcriptase hTERT:540-548. This peptide was reported to induce CTL that recognized tumor cells and transfectants that endogenously expressed telomerase. Therefore, we initiated a clinical protocol to evaluate the therapeutic and immunological efficacy of this peptide.

EXPERIMENTAL DESIGN

Fourteen patients with metastatic cancers were vaccinated with hTERT:540-548 emulsified in incomplete Freund's adjuvant.

RESULTS

In 7 patients, peripheral blood mononuclear cells collected after immunization recognized hTERT:540-548, whereas those collected before vaccination did not. However, none of these CTLs recognized tumors that endogenously expressed telomerase, and none of the patients had an objective clinical response. Several highly avid T-cell clones were generated that recognized T2 cells pulsed with <or=1 nm hTERT:540-548, but none of these recognized HLA-A*0201(+) hTERT(+) tumors or cells transduced with the human telomerase reverse transcriptase (hTERT) gene. Also, an antibody specific for hTERT:540-548/HLA-A*0201 complexes stained peptide-pulsed cells but not telomerase(+) tumors.

CONCLUSIONS

Our results are discordant with previous studies and those of a clinical trial that claimed peripheral blood mononuclear cells from patients vaccinated with peptide-pulsed dendritic cells lysed hTERT(+) tumors. However, our findings are consistent with a previous study that demonstrated that the hTERT:540-548 peptide is cleaved in the proteasome. These results suggest that hTERT:540-548 is not presented on the surfaces of tumor cells in the context of HLA-A*0201 and will not be useful for the immunotherapy of patients with cancer.

Epitope-based vaccines: an update on epitope identification, vaccine design and delivery

The basic premise of the epitope-based approach to vaccine development is that, in certain cases, the responses induced by the natural immunogen are not optimal, and can be improved upon by isolation or optimization of specific components of the response. For example, immunodominance is a key factor limiting the type and breadth of adaptive immunity. Recent advances in understanding the mechanisms of immunodominance thus represent an opportunity to further develop the epitope-based approach.

Phase I study of intranodal delivery of a plasmid DNA vaccine for patients with Stage IV melanoma

BACKGROUND

Based on the likelihood of transfecting large numbers of local antigen-presenting cells, a Phase I study in patients with Stage IV melanoma was conducted to determine the practicality, toxicity of, and immune responses to repeated infusions into a groin lymph node of escalating doses of a DNA plasmid encoding tyrosinase epitopes.

METHODS

Cohorts of 8 patients each received 200 microg, 400 microg, or 800 microg of DNA intranodally by pump over 96 hours every 14 days for 4 cycles. Blood was collected for immunologic assays and to measure plasmid in serum prior to treatment, 4 weeks later, and 8 weeks later. Scans and X-rays were performed at baseline and after 8 weeks.

RESULTS

Treatment was tolerated well, with only five patients demonstrating Grade 1-2 toxicity. Vaccine delivery by 96-hour infusions of plasmid into a groin lymph node resulted in only 1 episode of catheter leakage in 107 cannulations. Detection of plasmid in serum was rare and transient in two patients. Immune responses by peptide-tetramer assay to tyrosinase 207-216 were detected in 11 of 26 patients. No clinical responses were seen. Survival of the heavily pretreated patients on this trial was unexpectedly long, with 16 of 26 patients alive at a median follow-up of 12 months.

CONCLUSIONS

Infusion of a DNA plasmid vaccine into a groin lymph node was practical and well tolerated. Immune responses to a novel tyrosinase epitope were noted. Overall survival in this trial of heavily pretreated patients was unexpectedly long, with 16 of 26 patients alive after a follow-up of 12 months, favoring immune responders.

Hybrids of dendritic cells and tumor cells generated by electrofusion simultaneously present immunodominant epitopes from multiple human tumor-associated antigens in the context of MHC class I and class II molecules

Hybrid cells generated by fusing dendritic cells with tumor cells (DC-TC) are currently being evaluated as cancer vaccines in preclinical models and human immunization trials. In this study, we evaluated the production of human DC-TC hybrids using an electrofusion protocol previously defined for murine cells. Human DCs were electrically fused with allogeneic melanoma cells (888mel) and were subsequently analyzed for coexpression of unique DC and TC markers using FACS and fluorescence microscopy. Dually fluorescent cells were clearly observed using both techniques after staining with Abs against distinct surface molecules suggesting that true cell fusion had occurred. We also evaluated the ability of human DC-TC hybrids to present tumor-associated epitopes in the context of both MHC class I and class II molecules. Allogeneic DCs expressing HLA-A*0201, HLA-DR beta 1*0401, and HLA-DR beta 1*0701 were fused with 888mel cells that do not express any of these MHC molecules, but do express multiple melanoma-associated Ags. DC-888mel hybrids efficiently presented HLA-A*0201-restricted epitopes from the melanoma Ags MART-1, gp100, tyrosinase, and tyrosinase-related protein 2 as evaluated by specific cytokine secretion from six distinct CTL lines. In contrast, DCs could not cross-present MHC class I-restricted epitopes after exogenously loading with gp100 protein. DC-888mel hybrids also presented HLA-DR beta 1*0401- and HLA-DR beta 1*0701-restricted peptides from gp100 to CD4(+) T cell populations. Therefore, fusions of DCs and tumor cells express both MHC class I- and class II-restricted tumor-associated epitopes and may be useful for the induction of tumor-reactive CD8(+) and CD4(+) T cells in vitro and in human vaccination trials.

Stimulation of tumor-reactive T lymphocytes using mixtures of synthetic peptides derived from tumor-associated antigens with diverse MHC binding affinities

The use of reverse immunology may be necessary to identify new tumor-associated antigens, particularly for cancers, against which tumor-reactive T cell populations have been difficult to establish. One approach has been to screen peptides derived from a candidate antigen with high major histocompatibility complex (MHC) binding affinities for the induction of tumor-reactive T lymphocytes in vitro. However, many candidate antigens that are overexpressed in tumors are nonmutated self-proteins, and unlike foreign or mutated proteins, immunodominant epitopes may not be expressed at high density on the surface of tumor cells. Therefore, to identify tumor-associated epitopes, it may be necessary to screen large panels of peptides with wide ranges of MHC binding affinities. The current methodology of stimulating peripheral blood lymphocytes (PBL) from donors expressing the MHC molecule of interest with individual peptides is impractical for screening such large panels. Therefore, we evaluated the use of mixtures of peptides with variable MHC binding affinities for the induction of tumor-reactive T lymphocytes with the melanoma antigens gp100 and an alternate isoform of tyrosinase-related protein 2 (TRP2-6b) as models. A mixture of 10 known human leukocyte antigen (HLA)-A*0201-restricted peptides from gp100 induced melanoma-reactive cytotoxic T lymphoycte (CTL) from multiple patients with metastatic melanoma. The majority of these T cell populations recognized the known immunodominant epitopes gp100:209-217 and gp100:280-288, even though the HLA-A*0201 binding affinities of these peptides were much lower than other peptides in the mixture. Similarly, melanoma-reactive CTL were generated with a mixture of HLA-A*0201-restricted peptides from TRP2-6b, and these responses were directed against the previously identified tumor-associated epitopes TRP2-6b:180-188, TRP2-6b:288-296 and TRP2-6b:403-411. These results suggest that the use of peptide mixtures may facilitate the identification of new tumor-associated antigens through the application of reverse immunology.

Molecular anatomy of tyrosinase and its related proteins: beyond the histidine-bound metal catalytic center

The structure of tyrosinase (Tyr) is reviewed from a double point of view. On the one hand, by comparison of all Tyr found throughout nature, from prokaryotic organisms to mammals and on the other, by comparison with the tyrosinase related proteins (Tyrps) that appeared late in evolution, and are only found in higher animals. Their structures are reviewed as a whole rather than focused on the histidine (His)-bound metal active site, which is the part of the molecule common to all these proteins. The availability of crystallographic data of hemocyanins and recently of sweet potato catechol oxidase has improved the model of the three-dimensional structure of the Tyr family. Accordingly, Tyr has a higher structural disorder than hemocyanins, particularly at the CuA site. The active site seems to be characterized by the formation of a hydrophobic pocket with a number of conserved aromatic residues sited close to the well-known His. Other regions specific of the mammalian enzymes, such as the cytosolic C-terminal tail, the cysteine clusters, and the N-glycosylation sequons, are also discussed. The complete understanding of the Tyr copper-binding domain and the characterization of the residues determinant of the relative substrate affinities of the Tyrps will improve the design of targeted mutagenesis experiments to understand the different catalytic capabilities of Tyr and Tyrps. This may assist future aims, from the design of more efficient bacterial Tyr for biotechnological applications to the design of inhibitors of undesirable fruit browning in vegetables or of color skin modulators in animals.