Presence of Dysregulated Immune Recovery (IMD) Following Autotransplant May Change the Type of Predominant Serum Light Chain and Elevate the Level in Patients with Multiple Myeloma (MM).

Abstract 4870

It is well recognized that there is a period of transient mono- or oligo-clonal predominance of certain classes of immunoglobulins (Ig) following blood stem cell transplant due to limited repertoire of regenerating B lymphocytes. The phenomenon sometimes becomes a source of confusion for assessing response in MM patients after transplant. In the study, we sought to determine whether the IMD changes the type of predominant serum light chain or elevates the level, thereby making interpretations of the serum free light chain assay difficult. The study includes 53 MM patients (median age 60, range 37 – 77 years) who were uniformly treated, between September 2006 and May 2009, with induction chemotherapy, autotransplant following high-dose melphalan-based ablative therapy and post-transplant maintenance. Both conventional serum protein electrophoresis (SPEP) and the polyclonal antisera-based free light chain assay of the Binding Site (FLC assay) were serially obtained before and after transplant up to one year, at least once every 2 weeks. IMD is defined by an appearance of new mono- or oligo-clonal Ig in serum that later disappeared spontaneously. 24 patients had Ig G, 12 Ig A, 13 light chain only and 4 nonsecretory MM. 18 of 53 patients (34%) showed IMD in a median onset of 44 days (range 22 to 182) from the 1^st autotransplant, and 7 of 23 (30%) in 64 days (range 52 to 230) following the 2^nd autotransplant. The median duration of IMD was 51 (range 12 to 194) and 48 (range 15 to 318) days, following the 1^st and 2^nd transplant, respectively. Of the combined total of 25 cases with IMD, 18 (72%) showed Ig G kappa and Ig G lambda biclonal bands and 7 (28%) other monoclonal Ig, respectively. There was no case of different light chain only gammopathy. At the time of IMD following the 1^st transplant, 2 showed normal and 16 abnormal FLC assays. Of the 16, 3 showed different types of predominant light chains from that of the diagnosis, and 13 similar types. Following the 2^nd transplant, all 7 cases showed similar type of light chains. Of the 25 cases of IMD in the combined 76 cases of transplant, 22 cases were associated with the similar type of light chains whereas there were only 3 cases (12%) of different light chain predominance. There was no case of a different type of predominant light chain associated with the non-IMD cases (Fisher's Exact test, p = 0.01). Of the 22 cases of IMD associated with the similar type of light chain, 5 (20%) showed transient elevations in the light chain level > 2 x the pre-IMD values, with the median duration of elevations of 28 (range 7 to 64) days. The current study suggests that if IMD is suspected following transplant by SPEP, careful observation for at least a month but no immediate re-evaluation of disease status may be indicated even when the type or level of light chain changed. Further study is necessary to confirm the findings.