Tumor Microenvironmental Features and Outcome in Post-Transplant Lymphoproliferative Disorder

Background: PTLD comprises a diverse spectrum of hematological conditions, ranging from early lesions, characterized by reactive-like proliferations, to monomorphic lesions, resembling overt lymphoma. Â In most cases, the lesions are believed to arise as the result of reduced immune surveillance secondary to the use of immunosuppressive drugs post-transplant. This view is supported by the observation that PTLDs, particularly those characterized by early or polymorphic lesions, may regress spontaneously upon reduction of the immunosuppressive treatment. Studies in sporadic lymphomas have identified distinct microenvironmental characteristics, predictive of the clinical behavior, but data is scarce in the immunocompromised setting. Therefore, the aim of this study was to investigate the tumor microenvironment in a population-based cohort of PTLD.

Methods: We identified 108 PTLD patients diagnosed in the period 1994-2011. Of these, 62 cases had adequate tissue for tissue microarray construction. All biopsies were reviewed and classified according to the WHO 2008 criteria. Immunohistochemically stained sections were digitally quantified using Tissuemorph (Visiopharm Integrator System 4.0.3.0, Visiopharm, Denmark). Determination of optimal cut-off values of the area fraction (AF) was established by a ROC-curve. ROC analyses were performed in every disease entity and used for endpoint analyses.

Results: Themedian age was 45 yrs (range 2-77 yrs) with a M/F ratio of 3:1. The majority presented in stage I-II (61%), and B symptoms and extranodal disease were common features (40% and 42%, respectively). Most tissue samples were EBV-positive (85%). The EBV latency pattern was predominantly latency II (41%) or III (43%). The AF of galectin-1 (gal-1) positive cells was clearly correlated to latency type (p=0.0001), whereas FOXP3 and programmed death-1 (PD-1) did not show such correlation (fig 1).

Overall survival (OS) was significantly higher in cases with high levels of PD-1 expression, with 5-yrs OS of 39% (23-55%) and 69% (47-83%) for low and high levels, respectively (p=0.01). Expression levels of FOXP3 and gal-1 had no impact on OS in the total cohort (fig 1).

In the monomorphic setting, a low AF of FOXP3 positive cells was associated with an increased risk of progression (OR 6.1; 95% CI: 1.4-26.0). This did not, however, translate into an inferior OS (p=0.163).

To specifically characterize the tumor microenvironmental features of DLBCL-type PTLD with respect to cell of origin (COO), 30 evaluable cases were analyzed according to the Hans classifier; 10 (33%) were germinal center (GC) type and 20 (67%) of non-GC type. Cases of non-GC subtype had a significantly shorter time to PTLD of 1.16 yrs (CI: 0.64- 2.11), than those of GC-subtype (3.66 yrs; CI: 1.64- 8.16) (p=0.023) and a lower AF of gal-1 positive cells (p=0.042). The 5-yrs OS was 58% (32-77%) and 0% for non-GC versus GC-tumors, respectively (p=0.075). High levels of FOXP3 expression were associated with superior OS in the non-GC sub-group (p=0.04); gal-1 and PD-1 had no influence in the COO setting.

Conclusion: The present study is one of the few attempts to describe tumor microenvironmental features in PTLD and relate them to outcome. In a population-based PTLD cohort, we found that specific immune cell subsets were variably expressed in different PTLD subtypes, and that high expression of PD-1 (whole cohort) and FOXP3 (non-GC DLBCL only) correlated with significantly better outcome. Â

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