Clonal diversity of the T-cell population responding to a dominant HLA-A2 epitope of HER-2/neu after active immunization in an ovarian cancer patient

Natural antigen processing and presentation of antigen is thought to be important for the generation of a broad functional repertoire of antigen-specific T cells. In this study, the T-cell repertoire to an immunodominant human leukocyte antigen A2 (HLA-A2) binding peptide epitope of HER-2/neu, p369-377, was examined in a patient following immunization with a peptide-based vaccine consisting of helper peptides encompassing HLA-A2 peptide epitopes. The responding T-cell repertoire generated was both phenotypically and functionally diverse. A total of 21 p369-377 clones were generated from this patient. With the exception of two clones, all clones were CD3(+). Sixteen of the clones were CD8(+)/CD4(-). Five of the clones were CD4(+)/CD8(-), despite being generated with an HLA-A2 binding peptide. Nineteen of 21 of clones expressed the alpha beta-T-cell receptor (TCR). The remaining two clones expressed the gamma delta T-cell response (TCR). Selected alpha beta-TCR clones, both CD8(+) and CD4(+), could lyse HLA-A2 transfected HER2 overexpressing tumor cells and p369-377-loaded B-lymphoblastic cell line. In addition to their lytic capabilities these clones could be induced to produce interferon-gamma (IFN-gamma) specifically in response to p369-377 peptide stimulation. The 2 gamma delta-TCR clones expressed CD8 and lysed HLA-A2(+) HER-2/neu(+) tumor cells, but not HLA-A2(-) HER-2/neu(+) tumor cells. One of gamma delta-TCR clones also released IFN-gamma directly in response to p369-377 stimulation. These results suggest that a tumor antigen TCR, directed against a specific epitope, can be markedly polyclonal at multiple levels including CD4/CD8 and TCR.

Delayed type hypersensitivity response to recall antigens does not accurately reflect immune competence in advanced stage breast cancer patients

The development of delayed-type hypersensitivity (DTH) response to recall antigens has long been utilized as a measure of immune competence. It is assumed that because patients with advanced stage cancers exhibit multiple immune system defects they may not be responsive to immunization. We pre-selected patients with advanced HER-2/neu (HER2) overexpressing breast and ovarian cancers for enrolment into a phase I trial designed to evaluate the immunogenicity of a HER2 peptide vaccine based on the patient's immune competence as assessed by DTH skin testing to common recall antigens (Multitest CMI, Institut Merieux, Lyon, France). At the time of a positive DTH response to tetanus toxoid (tt) peripheral blood was obtained to measure T cell responses to tt. Of 53 patients evaluated, 38 (72%) were not anergic. Among the 15 (28%) who were, seven patients with advanced stage breast cancer were re-tested a median of 26 days (range 12-150 days) after receiving a tt bopster vaccination. Five of the seven had positive DTH responses when re-challenged with tt and six had peripheral blood tetanus specific T cell response with stimulation index >2.0. Thus, the majority of patients studied with advanced stage breast or ovarian cancer were able to mount a DTH response to common recall antigens. Moreover, a negative response by DTH testing to a battery of common recall antigens was not a reflection of the breast cancer patient's ability to mount a cell-mediated immune response to a vaccinated antigen, tt.

Generation of T-cell immunity to the HER-2/neu protein after active immunization with HER-2/neu peptide-based vaccines

PURPOSE

The HER-2/neu protein is a nonmutated tumor antigen that is overexpressed in a variety of human malignancies, including breast and ovarian cancer. Many tumor antigens, such as MAGE and gp100, are self-proteins; therefore, effective vaccine strategies must circumvent tolerance. We hypothesized that immunizing patients with subdominant peptide epitopes derived from HER-2/neu, using an adjuvant known to recruit professional antigen-presenting cells, granulocyte-macrophage colony-stimulating factor, would result in the generation of T-cell immunity specific for the HER-2/neu protein.

PATIENTS AND METHODS

Sixty-four patients with HER-2/neu-overexpressing breast, ovarian, or non-small-cell lung cancers were enrolled. Vaccines were composed of peptides derived from potential T-helper epitopes of the HER-2/neu protein admixed with granulocyte-macrophage colony-stimulating factor and administered intradermally. Peripheral-blood mononuclear cells were evaluated at baseline, before vaccination, and after vaccination for antigen-specific T-cell immunity. Immunologic response data are presented on the 38 subjects who completed six vaccinations. Toxicity data are presented on all 64 patients enrolled.

RESULTS

Ninety-two percent of patients developed T-cell immunity to HER-2/neu peptides (stimulation index, 2.1 to 59) and 68% to a HER-2/neu protein domain (stimulation index range, 2 to 31). Epitope spreading was observed in 84% of patients and significantly correlated with the generation of a HER-2/neu protein-specific T-cell immunity (P =.03). At 1-year follow-up, immunity to the HER-2/neu protein persisted in 38% of patients.

CONCLUSION

The majority of patients with HER-2/neu-overexpressing cancers can develop immunity to both HER-2/neu peptides and protein. In addition, the generation of protein-specific immunity, after peptide immunization, was associated with epitope spreading, reflecting the initiation of an endogenous immune response. Finally, immunity can persist after active immunizations have ended.

Immunization of cancer patients with a HER-2/neu, HLA-A2 peptide, p369-377, results in short-lived peptide-specific immunity

Ideally, vaccines should be designed to elicit long-lived immunity. The goal of this study was to determine whether HER-2/neu peptide-specific CD8+ T-cell immunity could be elicited using an immunodominant HER-2/neu-derived HLA-A2 peptide alone in the absence of exogenous help. Granulocyte macrophage colony-stimulating factor (GM-CSF) was used as adjuvant. Six HLA-A2 patients with HER-2/neu-overexpressing cancers received 6 monthly vaccinations with a vaccine preparation consisting of 500 microg of HER-2/neu peptide, p369-377, admixed with 100 microg of GM-CSF. The patients had either stage III or IV breast or ovarian cancer. Immune responses to the p369-377 were examined using an IFN-gamma enzyme-linked immunosorbent spot assay. Before vaccination, the median precursor frequency (range), defined as precursors per 10(6) peripheral blood mononuclear cell, to p369-377 was 0 (no range). After vaccination, the median precursor frequency to p369-377 in four evaluable patients was 0 (0-116). Overall, HER-2/neu peptide-specific precursors developed to p369-377 in two of four evaluable subjects. The responses were short-lived and not detectable at 5 months after the final vaccination. Immunocompetence was evident, because patients had detectable enzyme-linked immunosorbent spot responses to tetanus toxoid and influenza. These results demonstrate that HER-2/neu MHC class I epitopes can induce HER-2/neu peptide-specific IFN-gamma-producing CD8+ T cells. However, the magnitude of the responses were low, as well as short-lived, suggesting that CD4+ T-cell help is required for lasting immunity to this epitope.

Flt3 ligand as a vaccine adjuvant in association with HER-2/neu peptide-based vaccines in patients with HER-2/neu-overexpressing cancers

Dendritic cells (DCs) are potent antigen-presenting cells and have shown promise to function as "natural" vaccine adjuvants. Currently, most cancer vaccine trials using DCs generate autologous DCs ex vivo for each patient. Systemic treatment with Flt3 ligand (FL) results in a marked increase of DCs in tissues such as spleen and lymph nodes in mice and in the peripheral blood and skin of humans. In light of these observations, we questioned whether FL could be used systemically as a vaccine adjuvant to stimulate DC mobilization in vivo, circumventing the need to generate DCs ex vivo. Ten patients with HER-2/neu-overexpressing cancer were enrolled in a phase 1 study to receive a HER-2/neu peptide-based vaccine targeting the intracellular domain of the HER-2/neu protein. All patients received 20 microg/kg FL per day subcutaneously for 14 days. Five patients received the HER-2/neu peptide-based vaccine alone on day 7 of the 14-day cycle, and 5 patients received the vaccine admixed with 150 microg granulocyte macrophage-colony-stimulating factor (GM-CSF) on day 7 of the FL cycle. T-cell proliferative responses to HER-2/neu peptides and intracellular domain protein suggest that vaccine regimens including FL as an adjuvant were not effective in eliciting a significant HER-2/neu protein-specific T-cell proliferative response. However, including FL as a vaccine adjuvant was effective in boosting the precursor frequency of interferon-gamma-secreting HER-2/neu-specific T cells. The small sample size of each group, however, did not allow a statistically significant comparison of immune responses between the FL alone and FL with GM-CSF arms. Finally, vaccine regimens including FL as a vaccine adjuvant were associated with the development of apparent autoimmune phenomena in some patients.

Clinical translation of peptide-based vaccine trials: the HER-2/neu model

In the development of targeted cancer immunotherapies, the choice of antigen is obviously critical to the design of any therapeutic strategy, but particularly so for tumor vaccines, which must distinguish malignant cells from normal cells. Investigations a decade ago focused on mutated tumor antigens, or viral tumor antigens, with the belief that these foreign or abnormal proteins would be best recognized by the host immune system. Within the last 10 years, however, several tumor antigens have been identified on the basis of recognition by infiltrating T cells in tumor samples. Studies on melanoma, in particular, have revealed that in addition to some mutated tumor antigens, several aberrantly expressed normal proteins, as well as tissue-specific differentiation factors, are recognized by the host immune system. Similar studies in other solid tumors have revealed that certain oncogenes overexpressed in malignant cells, such as p53 and HER-2/neu, are also recognized by host T cells. Our group has been investigating the HER-2/neu oncogenic protein as a vaccine target in patients with HER-2/neu-overexpressing cancers. However, several issues unique to the design of human clinical trials of cancer vaccines must be addressed when translating preclinical experiments to human clinical trials. First, HER-2/neu protein expression can vary depending on the tumor type. How would expression differences impact clinical trial design? Secondly, what are the issues in clinical trial design that are critical to the successful execution of a phase I study of a peptide-based vaccine? Thirdly, what types and amounts of clinical material are readily available for immunologic analysis and can be obtained with little distress and risk to the patients enrolled in the study? Finally, what steps must be implemented for a laboratory assay to evolve to meet the validation criteria needed for application as an immunologic monitoring tool?

Immunologic monitoring of cancer vaccine therapy: results of a workshop sponsored by the Society for Biological Therapy

The Society for Biological Therapy held a Workshop last fall devoted to immune monitoring for cancer immunotherapy trials. Participants included members of the academic and pharmaceutical communities as well as the National Cancer Institute and the Food and Drug Administration. Discussion focused on the relative merits and appropriate use of various immune monitoring tools. Six breakout groups dealt with assays of T-cell function, serologic and proliferation assays to assess B cell and T helper cell activity, and enzyme-linked immunospot assay, tetramer, cytokine flow cytometry, and reverse transcription polymerase chain reaction assays of T-cell immunity. General conclusions included: (1) future vaccine studies should be designed to determine whether T-cell dysfunction (tumor-specific and nonspecific) correlated with clinical outcome; (2) tetramer-based assays yield quantitative but not functional data (3) enzyme-linked immunospot assays have the lowest limit of detection (4) cytokine flow cytometry have a higher limit of detection than enzyme-linked immunospot assay, but offer the advantages of speed and the ability to identify subsets of reactive cells; (5) antibody tests are simple and accurate and should be incorporated to a greater extent in monitoring plans; (6) proliferation assays are imprecise and should not be emphasized in future studies; (7) the reverse transcription polymerase chain reaction assay is a promising research approach that is not ready for widespread application; and (8)there is a critical need to validate these assays as surrogates for vaccine potency and clinical effect. Current data and opinion support the use of a functional assay like the enzyme-linked immunospot assay or cytokine flow cytometry in combination with a quantitative assay like tetramers for immune monitoring. At present, assays appear to be most useful as measures of vaccine potency. Careful immune monitoring in association with larger scale clinical trials ultimately may enable the correlation of monitoring results with clinical benefit.

Vaccination against the HER-2/neu oncogenic protein

The HER-2/neu oncogenic protein is a well-defined tumor antigen. HER-2/neu is a shared antigen among multiple tumor types. Patients with HER-2/neu protein-overexpressing breast, ovarian, non-small cell lung, colon, and prostate cancers have been shown to have a pre-existent immune response to HER-2/neu. No matter what the tumor type, endogenous immunity to HER-2/neu detected in cancer patients demonstrates two predominant characteristics. First, HER-2/neu-specific immune responses are found in only a minority of patients whose tumors overexpress HER-2/neu. Secondly, immunity, if detectable, is of low magnitude. These observations have led to the development of vaccine strategies designed to boost HER-2/neu immunity in a majority of patients. HER-2/neu is a non-mutated self-protein, therefore vaccines must be developed based on immunologic principles focused on circumventing tolerance, a primary mechanism of tumor immune escape. HER-2/neu-specific vaccines have been tested in human clinical trials. Early results demonstrate that significant levels of HER-2/neu immunity can be generated with active immunization. The T-cell immunity elicited is durable after vaccinations have ended. Furthermore, despite the generation of CD8(+) and CD4(+) T-cells responsive to HER-2/neu in a majority of patients, there is no evidence of autoimmunity directed against tissues that express basal levels of the protein. Cancer vaccines targeting the HER-2/neu oncogenic protein may be useful adjuvants to standard therapy and aid in the prevention of relapse in patients whose tumors overexpress the protein. Furthermore, boosting HER-2/neu-specific T-cell frequencies via active immunization may allow the ex vivo expansion of HER-2/neu-specific T-cells for use in adoptive immunotherapy, a therapeutic strategy directed against the treatment of established disease.

Adoptive T-cell therapy for the treatment of solid tumours

Solid tumours can be eradicated by infusion of large amounts of tumour-specific T-cells in animal models. The successes seen in preclinical models, however, have not been adequately translated to human disease due, in part, to the inability to expand tumour antigen-specific T-cells ex vivo. Polyclonality and retention of antigen-specificity are two important properties of infused T-cells that are necessary for successful eradication of tumours. Investigators are beginning to evaluate the impact of attempting to reconstitute full T-cell immunity representing both major T-cell subsets, cytolytic T-cells and T-helper (Th) cells. One of the more important and often overlooked steps of successful adoptive T-cell therapy is the ex vivo expansion conditions, which can dramatically alter the phenotype of the T-cell. A number of cytokines and other soluble activation factors that have been characterised over the last decade are now available to supplement in vitro antigen presentation and IL-2. Newer molecular techniques have been developed and are aimed at genetically altering the characteristics of T-cells including their antigen-specificity and growth in vivo. In addition, advanced imaging techniques, such as positron emission tomography (PET), are being implemented in order to better define the in vivo function of ex vivo expanded tumour-specific T-cells.

Immunologic targets for breast cancer

Breast cancer is an immunogenic tumor. Over the last decade, investigations have shown that patients with breast cancer have pre-existent immune responses, both humoral and cellular, against a variety of proteins expressed in their tumors. Researchers using genomic and proteomic techniques have defined dozens of proteins that may serve as immunologic targets in breast cancer patients. In addition, other investigators focusing on a more directed approach of evaluating well-defined breast cancer proteins that are immunogenic have begun to translate some of the candidate antigens into human clinical trials of immune-based therapies in breast cancer. Immunogenic proteins associated with breast cancer are abundant. The major experimental question now facing breast cancer immunologists is how to prioritize these many candidate antigens for further evaluation for clinical use.

Cancer vaccines targeting the HER2/neu oncogenic protein

Several advances in basic immunology over the last few years have forced a re-evaluation of cancer vaccine development. The most important finding has been that human tumors are immunogenic. The HER2/neu oncogenic protein is a tumor antigen. Existent antibody, helper T-cell, and cytotoxic T-cell immunity to HER2/neu have been detected in patients with cancer. The HER2/neu protein is an excellent therapeutic target for the immune system. Passive immunotherapy strategies, such as the infusion of monoclonal antibodies specific for HER2/neu, have been shown to be of clinical benefit in patients with HER2/neu-overexpressing malignancies. Inducing an active immune response by generating endogenous HER2/neu-specific antibodies and T cells may result in long-lived immunity and, hopefully, therapeutic benefit. In the majority of patients with pre-existent HER2/neu immunity, the antigen-specific antibodies and T cells detected are of low magnitude. Therefore, vaccine strategies aimed at boosting immunity already present may be effective in generating significant levels of HER2/neu-specific antibodies and T cells.

Identification of T helper epitopes from prostatic acid phosphatase

Helper T cells (Th cells) play a central role in the initiation and maintenance of immune responses, including antitumor immunity. The ability of Th cells in murine models to maintain and enhance the cytolytic efficacy of CD8+ CTLs has led to a renewed interest in identifying human tumor antigens recognized by Th cells. Prostatic acid phosphatase (PAP) is a prostate cancer-associated tumor antigen. A rodent model has demonstrated that PAP-specific CTLs can induce destructive prostatitis. Human MHC class I epitopes derived from PAP have been identified previously, and peptide-specific CTLs have been shown to be able to lyse an MHC-restricted prostate cancer cell line. In the current study, we sought to identify Th epitopes derived from PAP that might be used to elicit PAP-specific Th responses, ultimately in the context of human vaccines targeting PAP. Using peripheral blood mononuclear cells (PBMCs) from subjects with and without PAP-specific Th responses, we screened a panel of 10 potential peptide epitopes for peptide-specific T-cell proliferation. Four peptides, p81-95, p199-213, p228-242, and p308-322, were identified for which peptide-specific T-cell proliferation occurred in the majority of patient PBMC samples that also exhibited PAP-specific T-cell proliferation. PBMCs from patients with prostate cancer and without PAP-specific Th immunity were then cultured in vitro with these four peptides. Peptide-specific T-cell lines could be generated from two of the four peptides, p199-213 and p228-242, that also proliferated in response to PAP protein stimulation. The ability of these two peptides to elicit PAP-specific Th responses suggests that they represent naturally processed PAP-specific MHC class II epitopes.

Naturally occurring prostate cancer antigen-specific T cell responses of a Th1 phenotype can be detected in patients with prostate cancer

BACKGROUND

Cytotoxic T cells (CTL) are considered one of the primary effector cell populations in antitumor immunity. Recent studies, however, have demonstrated the critical importance of helper T cells (Th), specifically interferon gamma (IFN gamma)-secreting Th1 cells, either by supporting an appropriate CTL environment or by recruiting other effector cells. We evaluated whether patients with prostate cancer have naturally occurring Th-cell responses specific for two prostate cancer-associated antigens, prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP), and whether Th1-type responses to these antigens could be detected.

METHODS

Peripheral blood mononuclear cells (PBMC) were collected from 80 patients with prostate cancer and 20 male controls without prostate disease. Th-cell responses were evaluated by measuring antigen-specific proliferation. IFN gamma and IL-5 secretion in response to antigen stimulation was determined by enzyme-linked immunosorbent assay.

RESULTS

T cell proliferative responses specific for PSA and PAP could be detected in patients with prostate cancer. Six percent (5/80) of patients had T cell responses specific for PSA and 11% (9/80) for PAP. T cell responses specific for PSA were more prevalent in patients with metastatic disease (P = 0.02), whereas responses specific for PAP could be detected in patients irrespective of disease stage. IFN gamma-producing Th cells, specific for both PSA and PAP, could be identified in patients with prostate cancer.

CONCLUSIONS

Patients with prostate cancer can have detectable Th-cell responses specific for the prostate cancer-associated proteins PSA and PAP. The presence of antigen-specific Th1 immune responses in prostate cancer patients suggests that an immune environment capable of supporting antigen-specific CTL may exist in vivo. Prostate 47:222-229, 2001.

Expansion of HER2/neu-specific T cells ex vivo following immunization with a HER2/neu peptide-based vaccine

The identification and characterization of tumor antigens has facilitated the development of immune-based cancer prophylaxis and therapy. Cancer vaccines, like viral vaccines, may be effective in cancer prevention. Adoptive T-cell therapy, in contrast, may be more efficacious for the eradication of existing malignancies. Our group is examining the feasibility of antigen-specific adoptive T-cell therapy for the treatment of established cancer in the HER2/neu model. Transgenic mice overexpressing rat neu in mammary tissue develop malignancy, histologically similar to human HER2/neu-overexpressing breast cancer. These mice can be effectively immunized against a challenge with neu-positive tumor cells. Adoptive transfer of neu-specific T cells into tumor-bearing mice eradicates malignancy. Effective T-cell therapy relies on optimization of the ex vivo expansion of antigen-specific T cells. Two important elements of ex vivo antigen-specific T-cell growth that have been identified are (1) the preexisting levels of antigen-specific T cells and (2) the cytokine milieu used during ex vivo expansion of the T cells. Phase I clinical trials of HER2/neu-based peptide vaccination in human cancer patients have demonstrated that increased levels of HER2/neu-specific T-cells can be elicited after active immunization. Initiating cultures with greater numbers of antigen-specific T cells facilitates expansion. In addition, cytokines, such as interleukin-12, when added during ex vivo culturing along with interleukin-2 can selectively expand antigen-specific T-cells. Interleukin-12 also enhances antigen-specific functional measurements such as interferon-gamma and tumor necrosis factor-alpha release. Refinements in ex vivo expansion techniques may greatly improve the feasibility of tumor-antigen T-cell-based therapy for the treatment of advanced-stage HER2/neu-overexpressing breast malignancy.

Immunization with a HER-2/neu helper peptide vaccine generates HER-2/neu CD8 T-cell immunity in cancer patients

CD4 T-cell help is required during the generation and maintenance of effective antitumor CD8 T cell-mediated immunity. The goal of this study was to determine whether HER-2/neu-specific CD8 T-cell immunity could be elicited using HER-2/neu-derived MHC class II "helper" peptides, which contain encompassed HLA-A2-binding motifs. Nineteen HLA-A2 patients with HER-2/neu-overexpressing cancers received a vaccine preparation consisting of putative HER-2/neu helper peptides p369-384, p688-703, and p971-984. Contained within these sequences are the HLA-A2-binding motifs p369-377, p689-697, and p971-979. After vaccination, the mean peptide-specific T-cell precursor frequency to the HLA-A2 peptides increased in the majority of patients. In addition, the peptide-specific T cells were able to lyse tumors. The responses were long-lived and detectable for more than 1 year after the final vaccination in select patients. These results demonstrate that HER-2/neu MHC class II epitopes containing encompassed MHC class I epitopes are able to induce long-lasting HER-2-specific IFN-gamma-producing CD8 T cells.

Antibody immunity to prostate cancer associated antigens can be detected in the serum of patients with prostate cancer

PURPOSE

Several immune based therapies targeting prostate cancer associated proteins are currently undergoing clinical investigation. In general, however, little is known about the immunogenicity of prostate cancer or which prostate cancer associated proteins elicit immune responses. We determine whether patients with prostate cancer have antibody immunity to known prostate cancer associated proteins, what the prevalence of this immunity is and whether immunity to individual proteins is associated with the stage of disease.

MATERIALS AND METHODS

We evaluated the inherent humoral immune response against prostate specific antigen (PSA), prostatic acid phosphatase, p53 and HER-2/neu, all known prostate cancer associated proteins, in 200 patients with various stages of disease and male controls.

RESULTS

Antibody immunity to PSA was significantly different between the patient (11%, 22 of 200) and control populations (1.5%, 3 of 100, p = 0.02), and titers 1:100 or greater were particularly prevalent in the subgroup of patients with androgen independent disease (11%, 6 of 56). Antibody immunity to prostatic acid phosphatase and p53 was detected (5.5%, 11 of 200 and 6%, 12 of 200), and was not different from the control population (4%, 4 of 100, p = 0.57 and 7%, 7 of 100, p = 0.74). Antibody immunity to HER-2/neu was significantly higher in patients with prostate cancer (15.5%, 31 of 200) compared to controls (2%, 2 of 100, p = 0.0004), and titers 1:100 or greater were most prevalent in the subgroup of patients with androgen independent disease (16%, 9 of 56).

CONCLUSIONS

These findings suggest that prostate cancer is an immunogenic tumor. Moreover, for PSA and HER-2/neu the prevalence of antibody immunity was higher in patients with androgen independent disease, indicating that even patients with advanced stage prostate cancer can have an immune response to their tumor.

Immunity to WT1 in the animal model and in patients with acute myeloid leukemia

The Wilms' tumor (WT1) gene participates in leukemogenesis and is overexpressed in most types of leukemia in humans. WT1 is also detectable in many types of lung, thyroid, breast, testicular, and ovarian cancers and melanoma in humans. Initial studies evaluated whether immune responses to murine WT1 can be elicited in mice. Murine and human WT1 are similar. Thus, mouse models might lead to resolution of many of the critical issues for developing WT1 vaccines. C57/BL6 (B6) mice were injected with synthetic peptides from the natural sequence of WT1 containing motifs for binding to major histocompatibility (MHC) class II molecules. Immunization induced helper T-cell responses specific for the immunizing WT1 peptides and antibody responses specific for WT1 protein. Screening of multiple murine cancer cell lines identified 2 murine cancers, TRAMP-C and BLKSV40, that "naturally" overexpress WT1. Immunization with MHC class I binding peptides induced WT1 peptide-specific cytotoxic T-lymphocyte (CTL) that specifically lysed TRAMP-C and BLKSV40. WT1 specificity of lysis was confirmed by cold target inhibition. No toxicity was noted by histopathologic evaluation in the WT1 peptide-immunized animals. WT1 peptide immunization did not show any effect on TRAMP-C tumor growth in vivo. Immunization of B6 mice to syngeneic TRAMP-C elicited WT1-specific antibody, demonstrating that WT1 can be immunogenic in the context of cancer cells. To evaluate whether WT1 might be similarly immunogenic in humans, serum from patients with leukemia was evaluated for pre-existing antibody responses. Western blot analyses showed WT1-specific antibodies directed against the N-terminus portion of the WT1 protein in the sera of 3 of 18 patients with acute myeloid leukemia (AML). (Blood. 2000;96:1480-1489)

Pre-existent immunity to the HER-2/neu oncogenic protein in patients with HER-2/neu overexpressing breast and ovarian cancer

Immunomodulatory strategies, such as antibody therapy and cancer vaccines, are increasingly being considered as potential adjuvant therapies in patients with advanced stage breast cancer to either treat minimal residual disease or prevent relapse. However, little is known concerning the incidence and magnitude of the pre-existent breast cancer specific immune response in this patient population. Using the HER-2/neu oncogenic protein as a model, a well-defined tumor antigen in breast cancer, we questioned whether patients with advanced stage HER-2/neu overexpressing breast and ovarian cancers (III/IV) had evidence of pre-existent immunity to HER-2/neu. Forty-five patients with stage III or IV HER-2/neu overexpressing breast or ovarian cancer were evaluated for HER-2/neu specific T cell and antibody immunity. Patients enrolled had not received immunosuppressive chemotherapy for at least 30 days (median 5 months, range 1-75 months). All patients were documented to be immune competent prior to entry by DTH testing using a skin test anergy battery. Five of 45 patients (11%) were found to have a significant HER-2/neu specific T cell response as defined by a stimulation index > or = 2.0 (range 2.0-7.9). None of eight patients who were HLA-A2 had a detectable IFNgamma secreting T-cell precursor frequency to a well-defined HER-2/neu HLA-A2 T cell epitope, p369-377. Three of 45 patients (7%) had detectable HER-2/neu specific IgG antibodies, range 1.2-8.9 microg/ml. These findings suggest that patients with advanced stage HER-2/neu overexpressing breast and ovarian cancer can mount a T cell and/or antibody immune response to their tumor. However, in the case of the HER-2/neu antigen, the pre-existent tumor specific immune response is found only in a minority of patients.