Questions: Graft-Versus-Host Disease and Graft-Versus-Tumor Immunity

Question 1

A leukemia patient receives an allogeneic bone marrow transplant. To prevent GVHD, the transplant team thoroughly depletes T cells from the donor graft. The patient has no GVHD but relapses two years later. What is the most likely immunological explanation?

• A. T cell depletion inadvertently destroyed the patient's residual B cells, eliminating antibody-mediated anti-leukemia surveillance
• B. T cell depletion removed both the GVHD-causing alloreactive T cells and the GVT-effect T cells that would have killed residual leukemia cells, eliminating anti-tumor immunity along with the harmful response
• C. The conditioning regimen of chemotherapy and radiation was not intensive enough to eliminate all leukemia cells before transplant
• D. GVHD prevention immunosuppressants suppressed the patient's own reconstituting immune system after engraftment

Answer: (B)

This case illustrates the core GVHD/GVT dilemma. The donor T cells responsible for GVHD (attacking recipient tissues) and those responsible for GVT (attacking residual leukemia) are the same or overlapping populations of alloreactive T cells. Depleting T cells to prevent GVHD simultaneously removes the anti-leukemia immune surveillance. The clinical evidence for this is unambiguous: T cell-depleted transplants show dramatically lower GVHD rates but higher relapse rates. You cannot eliminate one effect without losing the other using simple T cell depletion.

Question 2

What makes GVHD fundamentally different from classic graft rejection (host-versus-graft disease)?

• A. Graft rejection is mediated by T cells, while GVHD is primarily mediated by antibodies from the recipient's B cells
• B. In graft rejection, the recipient's immune cells attack the foreign graft; in GVHD, donor immune cells in the transplanted graft attack the recipient's own tissues
• C. GVHD only occurs in solid organ transplants (kidney, liver), while graft rejection occurs in hematopoietic stem cell transplants
• D. Graft rejection is uniformly more severe and life-threatening than GVHD

Answer: (B)

Graft rejection and GVHD are mirror-image processes. In rejection, the recipient still has a functional immune system that recognizes the transplanted organ's MHC molecules as foreign and destroys it. In GVHD, the hematopoietic stem cell transplant contains mature donor T cells that survive and proliferate in the recipient — who has been immunosuppressed by conditioning — and those donor T cells recognize the recipient's tissues as foreign. The 'host' and 'graft' roles are reversed: the graft attacks the host. This is unique to transplants that transfer immune cells (bone marrow/stem cell transplants) rather than just parenchymal tissue.

Question 3

Patients who develop mild GVHD after allogeneic bone marrow transplantation for leukemia tend to have lower relapse rates than those who develop no GVHD at all.

• T. True
• F. False

Answer: True

This is one of the most important and counterintuitive clinical observations in transplantation medicine. Mild GVHD is associated with better leukemia outcomes because the same donor T cells causing the alloreactive tissue damage are also attacking residual leukemia cells. The GVT effect is real and powerful: patients with GVHD have statistically lower relapse rates. This observation is what established that GVHD and GVT are coupled through the same T cell populations, and it directly motivates the therapeutic challenge — suppressing GVHD enough to prevent organ damage while preserving enough T cell alloreactivity to prevent relapse.

Question 4

Acute GVHD primarily targets lymphoid organs (spleen and lymph nodes) because these are the sites where donor T cells first encounter and react to recipient alloantigens.

• T. True
• F. False

Answer: False

Acute GVHD targets three main organs, all characterized by high epithelial turnover: the skin (rash, blistering), the gastrointestinal tract (severe diarrhea, mucosal sloughing), and the liver (bile duct damage, jaundice). The pathophysiology begins with tissue damage from pre-transplant conditioning (chemotherapy, radiation), which releases inflammatory cytokines that create a pro-inflammatory environment. Donor T cells do encounter recipient antigens in lymphoid organs, but the downstream tissue attack falls on high-turnover epithelial tissues. The lymphoid organs are not the primary targets of the damage.

Question 5

Why does the GVT effect make GVHD management a therapeutic dilemma rather than a problem with a straightforward solution?

Model answer: Because the donor T cells that cause GVHD and those that provide the GVT anti-leukemia effect are the same alloreactive T cell population. Completely suppressing or depleting T cells eliminates GVHD but simultaneously removes the immune surveillance that destroys residual leukemia cells, leading to relapse. Insufficient immunosuppression allows GVHD to cause life-threatening organ damage (GI sloughing, liver failure, skin blistering). There is no simple 'off switch' for GVHD that does not also turn off GVT. Modern approaches try to selectively separate the two — using regulatory T cells to suppress alloreactivity against normal tissues while preserving anti-tumor reactivity, or using donor lymphocyte infusions to boost GVT in patients showing signs of relapse — but complete dissociation of GVHD from GVT remains an unsolved problem in transplantation medicine.

This dilemma is foundational to why allogeneic transplantation for leukemia involves such difficult tradeoffs. The cure mechanism (GVT) and the major complication (GVHD) share the same cellular machinery. Any intervention targeting one necessarily perturbs the other.