Tumor-Infiltrating T Cells Are Not Predictive of Clinical Outcome in Follicular Lymphoma.

Background: Follicular lymphoma (FL) has variable clinical outcomes. It has been suspected that tumor-infiltrating immune cells affect the biology and outcome of this disease. Using gene expression profiling and immunoperoxide tissue staining techniques, T cells and macrophages have been related to the survival outcome in some studies, but not others. In the current study, we used flow cytometry to analyze T cells and their subsets in follicular lymphoma biopsy specimens and determined whether these cell populations correlated with clinical features and outcomes.

Methods: Two hundred and eighty-nine follicular lymphoma patients (pt) presented from 1997 to 2003 underwent an excisional lymph node biopsy prior to any treatment. The median age of pt at diagnosis was 45.7 yrs, median follow-up was 8.6 yrs for living pts, and median survival was 15.7 yrs. All but 8 patients had stage III/IV disease, 5 had stage I/II, and 3 were unknown. The histological grades were: 162 (56%) grade 1, 112 (39%) grade 2, 13 (4.5%) grade 3 and 2 (0.5%) unknown. Among the 289 patients, 41(17%) had low FLIPI score, 150 (63%) intermediate, 48 (20%) high and 50 unknown. All biopsies were analyzed for CD20, CD3, CD4, CD8 and HLA-DR expression by single-parameter flow cytometry. The 289 pts were divided into a training set of 147 and a validation set of 142, stratified by age and era of diagnosis. We used these two factors to stratify the pts because age at diagnosis is the most important prognostic factor for survival, and, in our data set, the era of diagnosis had an impact on survival and on the time from diagnosis to first treatment. For our analysis, we began with the training set and used the percentages of each immune cell population as a continuous variable in a univariate analysis in relation to clinical features and outcomes. We chose 8 phenotypic variables: CD20, CD3, CD4, CD8, HLA-DR, CD4/CD3 ratio, CD8/CD3 ratio, and activated T cells [defined as (HLA-DR-CD20)/CD3]. Five parameters were used as clinical endpoints: overall survival, FLIPI score at diagnosis, the time from diagnosis to first treatment (defined as the time from the first treatment to second treatment), response to CVP as the first treatment and the duration of the benefit from the first treatment (defined as the time interval between initiation of first treatment and initiation of second treatment).

Results: The number of pt evaluable for each of the outcome parameters was as follows: 289 for time to first treatment and for overall survival, 239 for FLIPI scores, 164 for response to CVP and 129 for duration of the benefit from the first treatment., Of the 8 variables tested in the training set, only CD4/CD3 ratio and CD8/CD3 ratio were marginally significant for the survival endpoint, with p 0.034 and 0.088, respectively. None of the variables was significant for any of the other endpoints. A multivariate analysis yielded CD4/CD3 as the only significant predictor for survival. When CD4/CD3 was tested in the validation set, it yielded a p value of 0.48.

Conclusion: We find no evidence that the percentage of tumor-infiltrating T cells or their subsets is predictive of clinical outcome in follicular lymphoma. Any gene expression signature involving T cells that does relate to clinical outcome could therefore be a property of the activity of the cells rather than a simple reflection of their numbers.