Absence of retroviral vector-mediated transformation of gene-modified T cells after long-term engraftment in mice.

There is considerable concern regarding the transforming potential of retroviral vectors currently used for gene therapy, with evidence that retroviral integration can lead to leukemia in recipients of gene-modified stem cells. However, it is not clear whether retroviral-mediated transduction of T cells can lead to malignancy. We transduced mouse T cells with a Moloney murine retroviral gene construct and transferred them into congenic mice, which were preconditioned to enhance the engraftment of transferred T cells. Recipients were then observed long-term for evidence of cancer. Transferred T cells persisted in mice throughout life at levels up to 17% with gene copy numbers up to 5.89 x 10(5) per million splenocytes. Mice receiving gene-modified T cells developed tumors at a similar rate as control mice that did not receive T cells, and tumors in both groups of mice were of a similar range of histologies. Hematological malignancies comprised approximately 60% of cancers, and the remaining cancers consisted largely of carcinomas. Importantly, the incidence of lymphomas was similar in both groups of mice, and no lymphomas were found to be of donor T-cell origin. This study indicates that the use of retroviral vectors to transduce T cells does not lead to malignant transformation.

A103: An anti-melan-a monoclonal antibody for the detection of malignant melanoma in paraffin-embedded tissues.

Melan-A is a previously defined, melanocyte differentiation antigen, and an anti-Melan-A murine monoclonal antibody, A103, was recently developed by our group. In this study, we evaluated A103 immunoreactivity on formalin-fixed, paraffin-embedded tissues, exploring the potential of A103 in the diagnosis of metastatic melanoma. Seventy-five metastatic melanomas, 10 primary melanomas, and 10 benign melanocytic nevi were tested. The reactivity of A103 was compared with HMB-4, an anti-gp100 antibody. Results showed that all nevi were A103 positive, and most primary melanomas were A103 and HMB45 positive. Of 75 metastatic melanomas, 61 (81%) were A103 positive, and 56 (75%) were HMB45 positive. Of 19 HMB45-negative lesions, 8 were A103 positive; of 14 A103-negative lesions, 3 were HMB45 positive. Eleven metastatic lesions, as well as 2 of 10 primary melanomas, were dual negative. These negative cases consisted mainly of the spindle cell and desmoplastic variants. Of the positive cases, A103 showed homogeneous staining in a significantly higher proportion of cases than HMB45 (72% versus 52%). In addition, focal staining with less than 5% reactive tumor cells was seen more frequently in HMB45 (12 of 56) than in A103 (5 of 61). These results indicated that A103 can be used as a first-line antibody in the diagnosis of metastatic melanoma. Our results also showed that A103 reacted with angiomyolipoma, which is known to be HMB45 positive. Of normal tissues, unexpected A103 reactivity was observed in the adrenal cortex, granulosa and theca cells of the ovary, and Leydig cells of the testis. This A103 immunoreactivity in benign and neoplastic tissues of nonmelanocytic origin, the basis of which is unclear, could also be of potential diagnostic value.