Secondary lymphoid organs contribute to, but are not required for the induction of graft-versus-host responses following allogeneic bone marrow transplantation: a shifting paradigm for T cell allo-activation

Abstract

Graft-versus-host disease (GVHD) remains the major complication of allogeneic bone marrow transplantation (allo-BMT). GVHD fundamentally depends upon the activation of donor T cells by host antigen-presenting cells (APCs), but the precise location of these interactions remains uncertain. We examined the role of secondary lymphoid organs (SLO) in the induction of GVHD by using homozygous aly/aly mice that are deficient in lymph nodes (LNs) and Peyer's patches (PPs). Lethally irradiated, splenectomized, aly/aly (LN/PP/Sp-/-) mice and sham-splenectomized, aly/+ (LN/PP/Sp+/+) mice received BMT from either syngeneic (aly/aly) or allogeneic, major histocompatibility complex (MHC) disparate donors. Surprisingly, although LN/PP/Sp-/- allo-BMT recipients experience a survival advantage, they developed significant systemic and target organ GVHD that is comparable to LN/PP/Sp+/+ controls. Early after allo-BMT, the activation and proliferation of donor T cells was significantly greater in the BM cavity of LN/PP/Sp-/- mice compared to LN/PP/Sp+/+ controls. Donor T cells in LN/PP/Sp-/- mice demonstrated cytolytic activity in vitro, but Graft vs Leukemia (GVL) activity could be overcome by increasing the tumor burden. These data suggest that SLO contribute to, but are not required for, allogeneic T cell responses, and suggest that the BM may represent an alternative, albeit less efficient site for T cell activation following allo-BMT.

Figure 1

Aly/aly mice lack Peyer’s patches, but the allo-stimulatory capacity of their DCs is comparable to littermate controls. The small intestines from age-matched naïve wild-type C57BL/6, aly/+, and aly/aly mice were harvested, examined, and photographed using a Nikon digital camera alone or attached to a microscope using 10× magnification lens. Although readily apparent in both wild-type C57BL/6 and aly/+ heterozygote littermate controls, aly/aly mice lacked visible Peyer’s patches. (A) Splenic DCs were purified from wild-type C57BL/6, aly/+littermate controls, and aly/aly mice and used to stimulate purified, MHC disparate Balb/c T cells in an MLR as described in the Materials and Methods section. No differences in the ability to stimulate T cell proliferation (B) IFNγ production (C) or the generation of CTL effectors (D) were observed among groups. Data are expressed as mean±SEM and are representative of 1 of 3 comparable experiments. Wild-type C57BL/6 ▨ aly/+ ■ aly/aly compared to T cells only .

Figure 2

Splenectomized, aly/aly (LN/PP/Sp−/−) mice develop significant clinical and target organ GVHD following allo-BMT from MHC-mismatched Balb/c donors. Lethally irradiated, splenectomized aly/aly mice (LN/PP/Sp−/−) received BMT from syngeneic aly/aly or allogeneic Balb/c donors as described in the Materials and Methods section. Littermate, sham splenectomized aly/+mice (LN/PP/Sp+/+) served as allo-BMT controls. In some experiments, wild-type C57BL/6 recipients of C57BL/6 or Balb/c BMT served as additional negative and positive GVHD controls, respectively. The severity of GVHD was subsequently assessed by survival (A) and clinical score (B).◆ syngeneic, ■ C57BL/6, ▲ LN/PP/Sp+/+, ● LN/PP/Sp−/−. Target organ histopathology in the intestinal tract (C), liver (D), and skin (E) was also examined in surviving mice 6 to 7 weeks after BMT. Histology scores from naïve, untransplanted aly/aly mice are also shown. Data are expressed as mean±SEM from of 4 (survival and clinical score) or 3 (target organ pathology) different experiments. n = 12 to 18, (survival and clinical score) or 6 to 12 (pathology) per group; *P<.01 compared to syn controls. naïve aly/aly □; syn ; allo-C57BL/6 cont ▨; LN/PP/Sp+ ■; LN/PP/Sp−/− .

Figure 3

Splenectomized, aly/aly (LN/PP/Sp−/−) mice develop significant clinical and target organ GVHD following allo-BMT from MHC mismatched B10.BR donors. Lethally irradiated, splenectomized aly/aly mice (LN/PP/Sp−/−) received BMT from syngeneic aly/aly or allogeneic B10.BR donors as described in the Materials and Methods section. Littermate, sham splenectomized aly/+ mice (LN/PP/Sp+/+) served as allo-BMT controls. Wildt-ype C57BL/6 recipients of C57BL/6 of B10.BR BMT served as additional positive GVHD controls. The severity of GVHD was subsequently assessed by survival (A) and clinical score (B). ◆ syngeneic, ■ C57BL/6, ▲ LN/PP/Sp+/+ ● LN/PP/Sp−/−. Target organ histopathology in the liver (C) and intestinal tract (D) was also examined in surviving LN/PP/SP−/− allogeneic mice at 6 to 7 weeks after BMT. Data are expressed as mean ± SEM from of 3 (survival and clinical score) or 2 (target organ pathology) different experiments. n=12 to 18 (survival and clinical score) or 8 to 12 (pathology) per group; *p<0.01 compared to syngeneic controls. syn LN/PP/Sp−/− ■.

Figure 4

Early infiltration of donor T cells into the livers of LN/PP/ Sp−/− mice correlates with the severity of hepatic GVHD on day 7 after BMT. Lethally irradiated LN/PP/Sp−/− and LN/PP/Sp+/+ and wild-type C57BL/6 recipients received BMT as in Figure 2. Liver tissue was collected on day 7, and the severity of GVHD was determined as described in the Materials and Methods section. Data are presented as mean ± SEM, and were combined from 2 similar experiments. n = 6 to 10 per group. *P<.05, allo C57BL/6 and LN/PP/Sp+/+ versus syn; #P<.01, LN/PP/Sp−/− versus all groups. syn ; allo C57BL/6 ▨; LN/ PP/Sp+/+ ■; LN/PP/Sp−/− .

Figure 5

Division of donor T cells in bone marrow cavity and liver 3 days following BMT. T cells (10 × 10⁶) from B10.BR donors were stained with Vibrant CFDA SE and infused into lethally irradiated, LN/PP/Sp−/− or LN/PP/Sp+/+ recipients as described in the Materials and Methods section. Three days after transfer, single cell suspensions were prepared from the bone marrow cavity (A) or liver tissue (B), and cells were pooled, labeled, and analyzed by flow cytometry. Data are presented as percent of total cells collected from each tissue and are shown from 1 of 3 similar experiments.

Figure 6

Donor CD4⁺ and CD8⁺ T cells present in the bone marrow of LN/PP/Sp−/− BMT recipients are activated, produce cytokines, and are capable of killing allogeneic targets in vitro. T cells (10 × 10⁶) from B10.BR donors were infused into lethally irradiated, LN/PP/Sp−/− recipients as described in the Materials and Methods section. Three to 5 days after transfer, single cell suspensions were prepared from the bone marrow cavity and cells were pooled, labeled, and analyzed by flow cytometry for cell surface (A), intracytoplasmic cytokine production (B), mRNA expression (C) and cytolytic function against allogeneic (solid square) or syngeneic (solid circle) targets (D). Data shown are representative from 1 of 3 (A, B, D) or 2 (C) similar experiments (n = 3 to 4 animals per experiment).

Figure 7

Evaluation of GVL responses in LN/PP/Sp−/− following allo-BMT. Lethally irradiated, LN/PP/Sp−/− and LN/PP/Sp+/+ and wild-type C57BL/6 recipients received BMT from syngeneic or allogeneic, B10.BR donors as in Figure 3. On day 0, either 1000 (A) or 2000 (B) or 5000 (C) MBL-2 cells were added to the donor stem cell inoculum. Survival was monitored daily and the cause of each death after BMT was determined by postmortem examination and ascribed to either GVHD or leukemia as described in the Materials and Methods section. In each case, data are combined from 2 different experiments (n = 8 to 16 per group).