The tumor antigen 5T4 is frequently expressed at high levels on renal cell carcinoma (RCC) and other epithelial carcinomas. Surveys of normal tissues demonstrate abundant 5T4 expression on placental trophoblast cells with limited expression elsewhere. 5T4 is the target for a therapeutic cancer vaccine (MVA-5T4) that elicits 5T4-specific serological, proliferative, and CTL responses. However, the anti-tumor activity of 5T4-specific CTL has not been extensively characterized. CD8+ T cells from HLA-A2+ healthy donors (n=4) or RCC patients (n=2) were stimulated in vitro with the HLA-A2-binding nonamer peptides 5T417–25 or 5T497–105 and screened by flow cytometry with specific tetramers (TET). CD8+/TET+ T cell clones specific for 5T417–25 or 5T497–105 peptide were isolated from 4/6 and 1/4 donors respectively. A subset of clones specific for 5T417–25 was cytolytic for MVA-5T4 infected HLA-A2+ LCL target cells and for constitutively HLA-A2- and 5T4- expressing RCC tumor cell lines (including A498 RCC). In a xenoengraftment assay, the co-inoculation of a representative 5T417–25-specific CTL clone with A498 RCC tumors cells into immune deficient mice completely prevented growth of A498 tumors. Taken together, these data demonstrate high avidity CD8+ CTL able to recognize the naturally-processed 5T417–25 epitope on RCC tumor cells including putative tumor-initiating cells are present in peripheral blood of both healthy donors and RCC patients. CD8+ T cell immunity targeting 5T417–25 is therefore of substantial interest both as a potential target for further development of vaccination or adoptive cellular immunotherapy and for immune monitoring studies in association with nonspecific immunotherapies.

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Inhibitory mechanisms of erythropoiesis in 20 patients with pure red cell aplasia (PRCA) were investigated using the technique of in vitro hematopoiesis and an assay for human parvovirus. Complement-dependent serum inhibitors against late erythroid progenitors (CFU-E) were demonstrated in seven of 19 patients examined, and complement-dependent inhibitors against early erythroid progenitors (BFU-E) were demonstrated in three of these seven patients. Nonspecific and complement-independent inhibitors against CFU-E were thought to be associated with the etiology of PRCA in one patient. Human parvovirus-mediated erythropoietic suppression was demonstrated in a patient with complete remission of acute lymphoblastic leukemia complicated with marrow erythroid aplasia, whose serum showed a perfect inhibition against erythroid progenitor cells. T-cell-mediated erythroid suppression was not demonstrated in the patients examined. These findings reveal that erythroid aplasia is associated with complement-dependent serum erythropoietic inhibitor in some patients (36.8% in the present study) with PRCA, but it is difficult to identify the mechanism of erythroid aplasia in more than half of the patients with PRCA. In addition, our present study discovered the presence of parvovirus-mediated marrow pure red cell aplasia in one adult patient with acute lymphoblastic leukemia.