The Effect of Infusion of Polyclonal Immunoglobulin or Its Fragments in the Improvement of the Immune Reconstitution after Autologous Stem Cells Transplantation (ASCT) in a Murine Model.

Introduction: The immunoglobulin (Ig) is one of the most diverse molecules in nature, and its therapeutic potential, by stimulation of the immune system, has been widely studied/used. Its effect is manifest at the cellular and humoral compartments. However it is still to clarify the specific effect of each fraction of the molecule in the observed immune stimulation.

Aims:

1. To develop a murine model of ASCT that mimics the autologous transplant in humans

2. To study the independent effect of the various fractions of the immunoglobulin in the reconstitution of the immune system after ASCT.

Methods: In this study, we developed, de novo, a murine model of ASCT. Four groups of transplanted animals were established (weekly injections of: Ig (n=8) or Fab fragment (n=7) or Fc fragment (n=6) or saline (control, n=7)). The evolution of the immune reconstitution was monitored weekly and compared among groups by characterization of cellular fractions by flow cytometry, serum levels of Igs by ELISA and thymic function by quantification of TRECs (“T cell receptor excision circles”). The statistical analysis of the longitudinal data was performed by a linear-mixed effects model.

Results: We determined that a regimen of daily injections of G-CSF for 4 consecutive days produces a degree of mobilization of hematopoietic stem cells adequate for a donors/recipient ratio of 9 to 7, and to a standard engraftment extent. Regarding the recovery of cellular sub-populations among groups, the major differences occur up to the 6^th week (w) after ASCT. As soon as 2 w after ASCT the treated groups show higher counts of CD4+ T cells compared with control mice (p<0.05). The maximum number of CD4+ T lymphocytes was attained at 2 w after ASCT for mice treated with Fab and Fc and at 9 w for mice treated with polyclonal Ig and PBS. The recovery of CD4+ T lymphocytes in the treated groups was higher compared to control (p<0.001 for Fab, p<0.001 for Fc and p=0.001 for polyclonal Ig). For CD8+ T cells, the mice treated with Fc show, during all the follow up, superior values, being statistically significant when compared to PBS treated mice (p=0.003). The differences with the other groups vary with time. Regarding the recovery of CD19+ lymphocytes, the mice treated with Fab reveal, after the 7th w, superior counts compared to all the other groups (p<0.05). Treated groups (Fab and Fc) show higher values of serum IgM compared to control, as well as an earlier recovery of levels (p<0.05). In what concerns CD4+ naïve T cells, the group treated with polyclonal Ig shows an increased recovery during the first weeks of treatment compared with the other groups (p<0.05).

Conclusions and Discussion: The early treatment with polyclonal Ig or its fragments is highly beneficial for the recovery of CD4 and CD8 T lymphocytes (earlier recovery and higher cell counts). After the 6^th week after transplant there is a tendency for homeostasis. The increase of CD4+ naïve T cells with Ig treatment may well correspond to an increased thymopoiesis, as suggested by our previous studies.