Defects In Lymphocyte Subsets and Serological Memory Persist a Median of 10 Years After High Dose Therapy and Autologous Progenitor Cell Rescue for Malignant Lymphoma

From the Wessex Blood and Bone Marrow Transplant Registry, 130 patients (pts.) with malignant lymphoma, who had undergone HDT, and were known to be in an ongoing continuous remission for at least 3 years were identified and invited to participate with the aim of quantifying lymphocyte subsets and serological memory. Thirty-seven pts., median age 52 years (range 30–71) consented to study participation; their histologies comprised: diffuse large B-cell lymphoma, 32%; Hodgkin's disease, 27%; follicular lymphoma, 27%; other lymphomas, 14%. The median follow-up from the time of HDT to study entry was 10.6 years (range 3.0–20.2). All, except 4 pts., had received peripheral blood derived progenitor cells, which had been purged in 2 pts. An age matched population (median 56 years) of 14 healthy individuals (predominantly patient spouses) served as controls. Lymphocyte subsets in peripheral blood were assessed using multicolour flow cytometric analysis with a 16 antibody panel. Serum antibody levels to measles, mumps, rubella, HiB, tetanus and pneumococcus were determined by ELISA.

There was no significant difference in T, B and NK-cell populations between long-term follow-up pts. and controls, however even at median follow-up of 10 years there were persisting altered CD4⁺/CD8⁺ ratios with a reduced proportion of CD4⁺ cells in pts. compared to controls (median CD4⁺ 43% vs. 63% respectively; P<0.001). Naïve CD4+ cells were profoundly reduced in patients (P<0.001) yet effector memory and central memory CD4⁺ cells were higher in the pts. (P<0.001 and P=0.009 respectively).The effector memory RA population (intermediate between naïve and effector T-cells) were found in similar proportions between pts. and controls. Within the CD8⁺ population, the naïve population was reduced (P<0.001) with a corresponding increase in CD8⁺ memory cells in pts (p<0.001) however there was no difference in the level of central and effector memory CD8⁺ cells between pts. and controls. CD4⁺ T-cell numbers positively correlated with time form transplant, showing a continuous linear relationship. There were no significant differences in the proportion of memory and naïve B-cells between pts. and controls. Similarly there was no difference in marginal zone-like, class switch subtyes and mature plasmablasts proportions between the two groups. Uptake of revaccination following HDT was sporadic. Despite only 15 pts. (and only 1 pt receiving full course) being revaccinated, all patients demonstrated tetanus antibody levels above the minimal protective level. In two pts. who had received only a single dose of tetanus vaccine had antibody levels only just above the minimum. No pts. had been revaccinated against measles, mumps or rubella: 58%, 43% and 23% of pts respectively were below the equivocal serological level for immunity. No pt. had received pre HDT HiB vaccination and only 1 post HDT; 11% were below the minimal protective level. Four pts. had been vaccination against pneumococcus pre HDT and 13 pts. post: In 33% pts. antibody levels were below the minimum protective level.

Even at a median of 10 years following curative HDT, defects in lymphocyte subsets persist. The sustained reduction in naïve T-cell subsets, likely as a result of thymic incapacity, resulted in a peripheral T-cell population with a restricted TCR repertoire and the potential for impaired responses to novel antigenic stimuli many years after HDT. Other lymphocyte lineages however were able to fully reconstitute. Lack of serologically determined immunity was common, and the risk of incomplete vaccination scheduling demonstrated. In line with consensus statements, pts. following HDT should undergo full course revaccination or at least have assessment of their serological memory quantified to minimise the risk of infectious morbidity.

No relevant conflicts of interest to declare.