Conversion to sirolimus in kidney transplant recipients with squamous cell cancer and changes in immune phenotype

Abstract

Background: Conversion to sirolimus from calcineurin inhibitor- (CNI), azathioprine- (AZA) and mycophenolate-based regimens reduces the risk of development of squamous cell carcinoma of the skin (SCC) in kidney transplant recipients (KTRs). Sirolimus conversion may also be protective by permitting beneficial changes in immune phenotype. It is not known how sirolimus will affect immune phenotype in KTRs with SCC.

Methods: Thirty-two KTRs with SCC were enrolled into this single-blinded randomized study and 13 KTRs randomized to sirolimus (4-10 ng/mL) and prednisolone 5 mg/day.

Results: Six-month post conversion to sirolimus FOXP3(+) CD127(low)CD25(high)CD69(-), the number of T cells (putative Treg) increased significantly (P = 0.008). Natural killer (NK) and CD56(bright) NK cells also increased significantly (P = 0.039 and 0.02). T-cell number only significantly increased in those KTRs where CNI was ceased as part of the conversion to mammalian target of rapamycin inhibitors (mTORi's) (P = 0.031) implying CNI cessation rather than mTORi initiation induced an increase in T-cell number. Increases in the NK cell number was only significant in those KTRs where AZA was ceased (P = 0.040), implying AZA cessation rather than mTORi initiation caused the NK cell number to increase. At 6 months, sirolimus conversion reduces new SCC/year, rate ratio 0.49 (95%CI: 0.15-1.63), P = 0.276. On therapy analysis and intention-to-treat analysis over 24 months, the rate ratios were 0.84 and 0.87, respectively, and did not reach significance.

Conclusions: Conversion to mTORi from CNI may reveal a pre-existing high Treg phenotype by unmasking CNI inhibition of FOXP3 expression. Cessation of AZA leads to increased NK cell number. High FOXP3(+) T-cell number on conversion to mTORi may predict those KTRs who continue to accrue SCC.

Fig. 1.

Box plot (median, range) of changes in FOXP3⁺ T cells from the study entry (baseline) to various time points after randomization. Clear bars represent those kidney transplant patients not on sirolimus at that time point. Stippled box plots represent KTR converted to sirolimus and who stayed on therapy (n = 13 randomized to conversion, n = 11 at 3 and 6 months and n = 3 at 24 months). Assessment of changes from baseline to 6 months by Wilcoxon signed-rank test. Comparison between groups at 6 months Mann–Whitney two-tailed test.

Fig. 2.

Box plot (median, range) of changes in NK cell number from the study entry (baseline) to various time points after randomization. Clear bars represent those kidney transplant patients not on sirolimus at that time point. Stippled box plots represent KTR converted to sirolimus and who stayed on therapy (n = 13 randomized to conversion, n = 11 at 3 and 6 months and n = 3 at 24 months). Assessment of changes from baseline to 6 months by Wilcoxon signed-rank test. Comparison between groups at 6 months Mann–Whitney two-tailed test.

Fig. 3.

Box plot (median and range) of changes in FOXP3⁺ T cells from randomization to 6 months in those KTR converted to sirolimus (n = 13). ‘CNI pre’ represents those KTR on calcineurin (CNI)-based regimens prior to conversion to sirolimus. ‘No CNI’ pre represents those KTR not on calcineurin prior to conversion to sirolimus. Only KTR where CNI was ceased as part of conversion to sirolimus had a significant increase in FOXP3⁺ T cell numbers.

Fig. 4.

Box plot (median and range) of changes in NK cell numbers from randomization to 6 months in those KTR converted to sirolimus (n = 13). ‘No AZA pre’ represents those KTR not on AZA based regimens prior to conversion to sirolimus. ‘AZA pre’ represents those KTR on AZA prior to conversion to sirolimus. Only KTR where AZA was ceased as part of conversion to sirolimus had a significant increase in NK cell numbers.