*Purpose: Increased life expectancy in HIV+ patients has resulted in an increase in CKD leading to ESRD; and therefore renal transplantation in these individuals is of the utmost importance. The histology of transplant kidney biopsies (TxKBx) in this setting is understudied. The aim of the study was to evaluate the histologic characteristics of TxKBx in HIV+ patients who received HIV- kidney transplants at our institution. Furthermore, the hypothesis of allograft kidneys to harbor HIV infection and serve as a tissue reservoir is also investigated on a subset of biopsies.

*Methods: All consecutive HIV+ TxKBx (HIV- donor to HIV+ recipient) at UCSF from 8/1/2000 to 9/30/2018 were included. A total of 163 biopsies (46 protocol at 6 months post-transplant and 117 cause) from 92 patients were identified (79 males and 13 females; mean age: 51.1 years [8.75 SD]; 44 African-Americans, 31 Caucasians, 11 Hispanics, 5 Asians, and 1 Pacific Islander). Key histologic diagnoses and outcome data were collected. HIV viral RNA and DNA in situ hybridization (ISH) (ACD RNAScope^R and DNAScope^R) was performed on a select set of biopsies (n=10) with acute cellular rejection.

*Results: Key histologic diagnoses with alloimmune injury included acute cellular or antibody mediated rejection (n=36; 22.1%), chronic active antibody mediated rejection (n=7; 4.3%), and borderline change (n=48; 29.4%). Sixty two (38.1%) cases had non-alloimmune diagnoses including ATN (n=27), polyomavirus nephropathy (n=11), immune complex glomerulonephritis (n=6), tubulointerstitial nephritis (n=5), FSGS, NOS type (n=5), nephrocalcinosis (n=4), acute pyelonephritis (n=2), PTLD (n=1), and diabetic nephropathy (n=1). Among the 46 protocol biopsies at 6 months post transplant 27 (58.6%) had significant histologic findings including acute rejection (n=3; 6.5%), borderline change (n=14; 30%); polyomavirus nephropathy (n=4; 8.6%), and other (n=6; 13%). Follow-up was available in 87/92 patients. Overall outcome at time of follow-up showed: Alive with functioning graft: 61/87 (70.1%); Alive but with graft loss: 11/87 (12.6%); and Deceased: 15/87 (17.2%). None of the biopsies evaluated showed HIV viral RNA or DNA with ISH.

*Conclusions: In our institution, rates of acute rejection in HIV+ recipients are higher than historical rates of rejection seen in HIV- recipients. Glomerular diseases (recurrent or de-novo) are infrequent and no HIV associated nephropathy was identified in any of the biopsies. In situ hybridization showed no evidence of HIV infection (tissue reservoir) in the transplant biopsies with acute cellular rejection. Protocol biopsies at 6 months post transplant were helpful to diagnose subclinical diseases. Overall outcomes were favorable.

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