Developing an Algorithm for Monitoring Chimerism after Allogeneic Bone Marrow Transplantation - A Single Centre Experience.

Analysis of chimerism for the evaluation of engraftment and rejection after allogeneic stem cell transplantation is now standard practice (ASCT). The most common technique used is PCR amplification of short tandem repeats (STRs) and variable number of tandem repeats (VNTRs). Data on informativeness of various VNTRs or STRs in HLA identical recipient donor pairs in a population is essential to establish a scheme of sequential testing. To determine the informativeness in our population, we screened five STRs namely FES, THO 1, VWA, ACTBP2, and F13A1 and 1 VNTR, APOB, in allogeneic bone marrow transplant patients with their HLA identical donors. Samples from 310 patients who underwent haematopoietic stem cell transplantation (HSCT) during the period 1993–2005 were analyzed. All donors were HLA identical siblings or related family members of the patient. Of the 310 patients, 120 (39%) were from southern India, 88 (28%), 25(8%), and 59 (19%) from northern, eastern and western parts of India respectively. Seventeen (5%) patients were from other countries (Maldives (n=4), Oman (n=4), Sri Lanka (n=2), Singapore (n=1), Mauritius (n=1), Pakistan (n=3), Bhutan (n=2)). For 15 (5%) of these 310 patients only amelogenin PCR results were available. The other 295(95%) patients and donors were studied by PCR for one or more of the polymorphic repeat sequences, (STRs or VNTR) namely FES, THO 1, VWA, ACTBP2, F13A1 and APOB. Of all the six markers used THO1 was the most informative (55%) and F13A1 the least (20%). Informativeness of the markers THO1+VWF, THO1+VWF+ACTBP2, THO1+VWF+ACTBP2+FES was 79, 87, and 92 percent respectively. By combining one, two or three markers, we could discriminate between 68 to 92 percent of the patient donor pairs. Addition of marker APOB to this panel discriminated 95% of the HLA identical patient donor pairs. Usage of Genescan analysis in practice to evaluate chimerism status has improved the utility of these markers from 95% to 97%. Using a combination of all these markers along with a polymorphic marker in the b-globin gene and Y chromosome specific amelogenin marker, we were able to discriminate 99% of the patient donor pairs. We have established an algorithm for evaluating chimerism in the Indian population using molecular markers in 310 patients and their HLA identical related donors. This data may be useful for transplant centers in adopting a strategy for evaluating chimerism following HLA identical ASCT.