LBP20: RELEVANCE OF STRONG POSITIVE DONOR SPECIFIC ANTIBODIES AND FLOW CROSSMATCH WHILE C1q TEST NEGATIVE IN RENAL TRANSPLANTATION

Aim In this study we present a case of a kidney recipient with pre-formed high titer anti donor DSA to one allelic mismatch antigen of a sibling donor. Pre-transplant the DSA appeared to be clinically significant based on strong positive crossmatch (XM) testing in both T- and B cell XM. Methods HLA typing is performed by SSO for low/intermediate resolution and SSP for high resolution. DSA is determined by One Lambda BScreen Single Antigen and C1q Screen assay. T and B cell IgG XM is performed by CANTO flow cytometer, where our cut-off for positive XM is determined based on normal human studies. Results Both donor recipient pairs were typed using low resolution class I and high resolution class II HLA typing. Five out of the twelve alleles (−A ∗ 31, B ∗ 51, DRB1 ∗ 11:01, DQA1 ∗ 05:05 and DQB1 ∗ 03:01) were considered the mismatched antigen based on the available data. Flow crossmatch result was Positive for bothT (+209 MCS) & B (+224 MCS) cell IgG flow crossmatch. DSA titer for the allelic mismatched antigen, B ∗ 51 was 10360 MFI. C1q-SA was despite high DSA titer and crossmatch clear negative. Anti- A ∗ 31, DRB1 ∗ 11:01, DQA1 ∗ 05:05 and DQB1 ∗ 03:01 were negative based on our cut off. The Kidney was transplanted and functioned immediately and continues to function well one month after transplantation. No modifications have been made in the standard immunosuppressive protocol used in our hospital (Induction: Basiliximab and Methylprednisolon; Maintenance: Mycophenolate mofetil, Prednisone and Tacrolimus) and the patient is without any signs of AMR. Conclusion The interpretation of DSA, flow crossmatch in this case was more accurate and predictive when result of solid phase antibody testing was considered along with the high resolution HLA typing. However, further studies and more data in C1q are needed allow renal transplantation and clarify the clinical relevance in patients with high DSA titers with positive crossmatch and negative C1q Testing.