Recipient T-Cell Repertoire Diversity after Double Umbilical Cord Transplantation Correlates with Non-Relapse Mortality and Survival

Complications of allogeneic stem cell transplant, such as infection, relapse and GvHD, are linked to failure of balanced immune reconstitution.� Early quantification of immunologic function is crucial to identify those at risk and institute pre-emptive therapies.� We hypothesize that T-cell receptor (TCR) diversity after double umbilical cord blood transplantation (dUCBT) will predict clinical outcomes.� Methods: 42 adult dUCBT recipients received fludarabine, melphalan, ATG with tacrolimus/sirolimus as GvHD prophylaxis.� TCRb CDR3 regions were amplified from unsorted PBMCs and sequenced using the ImmunoSeq platform (Adaptive Biotechnologies) at 3, 6 and 12 months after dUCBT.� Samples analyzed had predominantly donor T-cell chimerism and no morphologic relapse.� We analyzed 34 samples at 3 mos, 26 at 6 mos and 23 at 12 mos.� Entropy/Shannon's diversity index and richness/Fisher's alpha diversity were calculated from number and frequency of TCRb sequences and normalized for sequencing depth.� Higher entropy and richness, measures of uncertainty and unseen species within a complex population, reflect increased diversity.� Results: Median age was 52 years (19-67).� 57.1% were in remission at dUCBT.� Primary indications for dUCBT were AML, NHL and MDS. Median follow-up among survivors was 47 months (18-91). �4-year OS was 41%; 4-year PFS was 26%. �As a whole, dUCBT recipients increased entropy and richness of their T cell repertoire in the first year.� We categorized subjects into 3 groups: relapse, NRM, or alive with neither event.� In the NRM cohort, median entropy and richness values rose slightly from 3 to 6 mos then fell at 12 mos.� In comparison, median entropy and richness were higher in the no event cohort between 3 and 12 mos and rose substantially to diversity levels found in healthy donors.� (p=0.01, 0.09, 0.004 for entropy at 3,6,12 mos; p=0.06, 0.11, 0.006 for richness at 3,6,12 mos). (Figure) �Entropies of subjects who relapsed did not differ from those of the no event cohort (not depicted).� In a similar analysis, entropy values for subjects with chronic GvHD fell between 3 and 12 mos and were significantly lower than in subjects without any cGvHD, relapse, or NRM at 12 mos (median entropy 5.9 vs 12.3, p=0.04).� In multivariable analyses controlling for age, patient sex, disease status, and diagnosis, high entropy was associated with lower NRM (HR 0.68, p<0.001), PFS (HR 0.79, p=0.009) and OS (HR 0.73, p=0.005). �High richness (log10 transformed) was associated with lower NRM (HR 0.3, p<0.001) and OS (HR 0.30, p=0.0003).� Conclusion: T-cell repertoire diversity as early as 3 months after dUCBT is significantly lower in subjects who eventually experience NRM or cGvHD and does not expand with time after transplant.� These quantitative predictive indices may be used to identify dUCBT recipients who merit more intensive monitoring or prophylactic strategies against infection and GvHD.