Eradication of Recipient CMV Specific T Cells by Donor Lymphocyte Infusion Does Not Impair Protective Immunity In Patients Transplanted with a CMV Negative Donor Due to An Early Donor Derived Primary CMV Specific T Cell Response

Abstract 834

Previous studies have demonstrated that shortly after T cell depleted (TCD) allogeneic stem cell transplantation (alloSCT) CMV specific T cells in a CMV positive recipient transplanted with a CMV negative donor (R+D-) are of recipient origin. Development of de novo donor CMV specific T cells is thought not to occur during the first 6 months after TCD alloSCT. Donor lymphocyte infusion (DLI) to prevent leukemic relapse may induce allo-immune responses against recipient hematopoietic cells, and thereby eradicate protective CMV specific T cells of recipient origin. It has been hypothesized that following DLI in R+D- patients eradication of protective recipient CMV specific T cells may result in CMV disease. We studied CMV reactivation and CMV disease in 25 R+D- patients treated with DLI after TCD alloSCT. DLI was administered at 210 (median, range 41–689) days after transplantation (Tx). Overall chimerism decreased from a median of 15% (0%-63%) recipient origin prior to DLI to 1% (1%-77%) 3 months after DLI. Ten patients developed a CMV reactivation after DLI. The CMV reactivation required treatment in 3/10 patients. One patient developed CMV pneumonia. This patient received DLI very early (41 days) after Tx because of refractory disease. Since apparently DLI at 6 months after Tx was not associated with development of CMV disease, we hypothesized that CMV viraemia was controlled by the development of de novo donor derived CMV specific T cells. To investigate whether a primary immune response of donor origin had developed prior to or following DLI, we analyzed the origin of CMV specific T cells from 10 R+D- patients at 6 months after Tx and before and after DLI. Thawed PBMC were stimulated with overlapping 15-mer peptides from CMV derived proteins pp65 and IE1. Subsequently, activated CD137+ CD4 and CD8 T cells were isolated by FACS sorting. DNA was isolated for chimerism analysis using donor and recipient informative short tandem repeats-PCR. Patients had received DLI at a median of 253 days (181-699) after Tx. At 6 months after Tx (prior to DLI at a median 180 (149-301) days after Tx) donor CMV specific T cells were already present in 5/10 patients with a median of 98% (8%-100%) donor origin in CMV specific CD4 T cells and 97% (1%-100%) donor origin in CMV specific CD8 T cells. In 3 of these 5 patients donor CMV specific T cells were present as early as 3 months after Tx, CMV specific CD4 T cells in 2 patients (39% and 99% donor origin) and CMV specific CD8 T cells in 1 patient (76% donor origin). In 1 patient only recipient CMV specific T cells were found. In 1 patient with recurrent CMV reactivations no CMV specific T cells were present. Recipient CMV specific T cells were detected in 9/10 patients at 3 months after Tx, demonstrating the protective immunity to CMV disease by these residual T cells shortly after TCD alloSCT. At 6 months after Tx CMV specific T cells were still completely of recipient origin in 5 patients. One patient eventually developed donor CMV specific T cells prior to DLI at day 407. In 4 patients, CMV specific T cells were completely of recipient origin at time of DLI. In these 4 patients, the recipient CMV specific T cells were undetectable 3 months after DLI, demonstrating the eradication by DLI. However, the absolute number of donor CMV specific CD4 and CD8 T cells increased immediately following DLI. Donor CMV specific T cells increased from undetectable to 32*10E⁶/L (8– 40*10E⁶/L) and 59*10E⁶/L (34-95*10E⁶/L) respectively, illustrating that a primary donor derived CMV specific immune response had developed shortly after administration of DLI. To test whether recipient CMV specific T cells could persist for a prolonged time after TCD alloSCT in the absence of DLI we analyzed 5 additional patients who did not receive DLI. In 4/5 untreated patients, recipient CMV specific T cells were present at 2 years after TCD alloSCT (CMV specific CD4 32% (10%-87%) and CD8 98% (66%-100%)) compared to 1/10 treated patients (p=0.017). In conclusion, although DLI can eradicate recipient CMV specific T cells, it is safe to administer DLI 6 months after Tx to R+D- patients. In contrast to previous assumptions, we demonstrated that a donor primary immune response can develop within 6 months after Tx and that eradication of recipient T cells will then not lead to loss of immunity.