RARE HLA ALLELES IN RENAL TRANSPLANT CANDIDATES

In renal transplant candidates an increase of the uncommon HLA alleles due to immigration flow growth was observed. Humoral immune response often determines the production of a broad antibodies pattern due to the recognition of epitopes specific of the mismatched HLA molecules. So, factors like rare alleles should make difficult the finding of a suitable donor. We analyzed the presence of rare HLA alleles in 934 renal transplant candidates. High resolution PCR-SSP technique was performed to confirm the rare HLA alleles. A total of 20 rare/very rare alleles (2.1%) was found. We reported the following interesting alleles: A*02:11 (af = 0.25%) detected in an Asian patient differs from other A*02 alleles by Threonine vs Isoleucine and Histidine vs Aspartic substitutions at position 73 and 74 respectively; B*14:06 (af = 1.96%) detected in an Italian patient differs from other B*14 alleles by Tryptophan vs Arginine substitution at position 97; B*15:38 (af = 1.00%) detected in an Asian patient differs from other B*15 alleles by Histidine vs Tyrosine substitution at position 171; B*44:29, (af = 0.75%) detected in an Italian patient differs from other B*44 alleles by Aspartic acid vs Leucine and Alanine vs Threonine substitutions at position 156 and 158 respectively; DQB1*03:05 (af = 0.29%) detected in an Italian patient differs from other DQB1*03 alleles by Leucine vs Glicine substitution at position 26. These amino acid substitutions can determine, in sensitized patients, the production of a wide antibody pattern specific for all the mismatched HLA molecules sharing the same amino acid. An high resolution typing of HLA alleles, providing amino acid sequence information, could lead to identify epitopes that play the role of alloantigens and could represented an important step in transplant risk assessment.