OR19

Aim HLA-C∗04:09 N is characterized by a point deletion at nucleotide position 1095 in exon 7. This mutation results in a frame shift and causes the addition of 32 extra amino acids and the loss of cell surface expression (Balas A., et al. Tissue Antigens 2002;59:95–100). The goal of this study was to determine the frequency of the B∗44:03-C∗04:09 N bearing haplotype in leukemia patients treated at MDACC. Method Patients were typed for both HLA Class I and Class II using PCR-SSOP and PCR-SBT methodologies. The HLA-C∗04:09 N allele was resolved using PCR-SSP method. Results We identified and evaluated 300 consecutive patients with various forms of leukemia treated at our center carrying the HLA-B∗44:03-C∗04:01:01G typing with the inclusion of C∗04:09 N allele (2.2% of the total patient population). Of the 300 B∗44:03-C∗04:01:01G bearing patients, 21 were identified as HLA-C∗04:09 N (7%), which accounted for 0.15% in the entire patient population. Discussion Of the 21 patients bearing HLA-B∗44:03-C∗04:09 N alleles, 9 had haplotype assigned. Five of them (55.6%) carrying the haplotype of HLA-A∗23:01-C∗04:09 N-B∗44:03:01-DRB1∗07:01-DRB4∗01:01-DQB1∗02:02 and 2 others carrying the same haplotype but with different HLA-A alleles (Table 1). The study explored the frequency of HLA-C∗04:09 N in the presence of B∗44:03 in leukemia patients. The identification of this null allele would be important in HLA matching for patients in need of stem cell transplant. Misidentification of a patients null allele could impact graft outcome with a mismatched donor carrying the expressed allele or visa versa.