Analysis of CD34(+) cell subsets in stem cell harvests can more reliably predict rapidity and durability of engraftment than total CD34(+) cell dose,but steady state levels do not correlate with bone marrow reserve

In peripheral blood stem cell transplantation (PBSCT), the number of CD34() cells transplanted has been shown to correlate well with both rapidity an d durability of engraftment. However, it is clear that engraftment does not necessarily correlate with total CD34(+) cell numbers in some patients. Co nsequently, there is increasing interest in evaluating the role of CD34(+) subsets in haemopoietic recovery as a more accurate marker of harvest quali ty. We analysed the numbers of CD34(+) cell subsets, namely Thy-1(+), L-Sel ectin(+) and CD38(-), and correlated this with engraftment in 86 patients u ndergoing PBSCT. Adequate engraftment was defined as being a platelet count greater than 50 x 10(9)/l and a neutrophil count greater than 1.0 x 10(9)/ l. CD34(+)L-Selectin(+) provided the best prediction of engraftment rapidit y; although the improvement over total CD34(+) cell dose was minor. Only th e dose of CD34(+)Thy-1(+) cells transplanted correlated with durable engraf tment. The probability of adequate 3-month engraftment increased with the d ose of CD34(+) cells transplanted, but 10% of patients receiving > 5 x 10(6 )/kg still showed poor engraftment at 3 months. However, all patients recei ving > 2.5 x 10(5)/kg CD34(+)Thy-1(+) showed adequate engraftment at this t ime point. We also demonstrated that CD34(+)Thy-1(+) progenitors were restr icted to the bone marrow under normal conditions and, during stem cell mobi lization, their kinetics generally paralleled total CD34(+) numbers.