Analysis of HLA class Ia transcripts in human leukaemias

Several leukaemia-specific antigens have been discovered in the recent past, which raised the possibility for T-cell-based immunotherapy for leukaemia. However, failure of such approaches involving interleukin-2 and/or T-cell-based immunotherapy indicated the importance of investigation of the human leucocyte antigen (HLA) status of the haematopoietic malignant cells. Considerable number of reports indicate that both HLA class I and class II are down-regulated in different cases of leukaemias, enabling them to evade immuno-surveillance. However, locus-specific down-regulation in leukaemia has not been widely investigated, although majority of cytotoxic T lymphocyte (CTL) responses are modulated by HLA-A and HLA-B, whereas expression of only HLA-C is unable to block natural killer (NK)-cell-mediated cytotolysis. Therefore, using RT-PCR, we have investigated the HLA class I transcriptional expression in a locus-specific manner, along with HLA-associated accessory molecules beta2-microglobulin and transporter-associated antigen processing molecule (TAP1). Our data suggest that in several newly diagnosed untreated leukaemic patients, HLA-C and beta2-microglobulin are expressed, but not the locus HLA-A or -B. Moreover, TAP1 and beta2-microglobulin were observed to be down-regulated in a number of cases of leukaemia. Our flow cytometric analysis of HLA-ABC also indicates a decrease in mean fluorescent intensity but no complete loss in surface expression of HLA class Ia on the leukaemic cells. Therefore, the observed low surface expression of HLA-ABC may be due to the down-regulation of transcription of HLA-A or -B itself and/or transcriptional suppression of the accessory molecules.