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Acute graft versus host disease (aGVHD) is mediated by allogeneic T cell responses. We hypothesized that peripheral blood expansion of activated effector memory T cell populations (TEM) following allogeneic hematopoietic cell transplantation (HCT) would serve as a useful predictor of aGVHD.
Methods
T cells were characterized in peripheral blood samples from 16 consecutive pediatric allogeneic hematopoietic cell transplant (HCT) recipients. Samples were collected prior to transplant and weekly following HCT until day +42. Samples were incubated with fluorochrome-conjugated monoclonal antibodies directed against CD3, CD8, CD38, CD45RA and CCR7, followed by red cell lysis and fixation. Samples were analyzed by flow cytometry on a FACSCanto ll flow cytometer (BD Biosciences). Data was analyzed using FCS Express (De Novo Software). TEM were defined as CD3+ lymphocytes which lacked expression of CD45RA and CCR7. CD38 was used as a marker of activation.
Results
Patients had less than 65% of CD8+ CD38 bright TEMs prior to transplant except for 1 patient with HLH who had 99.8%, and was excluded from analysis. Patients who developed aGVHD (n=5), engraftment syndrome (n=2), or neither (n=8) were observed to develop median maximum expansions of CD8+ CD38bright TEM prior to or on the day of diagnosis of aGVHD, or before day +42, of 49 cells/mcl (range 21-87), 5 cells/mcL (range 0.3-34) and 98cells/mcL (range 0.04-197), respectively (p=0.02, GVHD versus neither GVHD nor engraftment syndrome). We observed that an absolute number of CD8+ CD38 bright TEM greater than 20cells/mcL was predictive of aGVHD with sensitivity of 100%, specificity of 80%, and a negative predictive value of 100%. The cumulative incidence of aGVHD in patients with greater than 20 CD8+ CD38 bright TEMs/mcL was 71%, and in patients with less than 20cells/mcL, 0% (p<0.01).
Conclusion
Quantification of peripheral blood CD8+ CD38 bright TEM is a novel predictor of aGVHD.