Prashanth Vallabhajosyula has spent years chasing a problem that haunts lung transplant patients: the need for repeated surgical biopsies to detect organ rejection, a procedure that can cause bleeding, collapsed lungs, and other serious complications. Now, working from Washington University School of Medicine, he and his team may have found a way out—a simple blood test using tiny molecular packages released by immune cells that could replace those invasive procedures altogether.
Lung transplants carry an unfortunate distinction. Across all solid organ transplants, they rank among the highest for acute cellular rejection (ACR), the immune system's attack on the transplanted organ. Patients have historically needed multiple surgical biopsies to continuously monitor for signs of rejection, each procedure carrying real risks. That burden falls on people already facing long odds: approximately 60 percent of lung transplant recipients survive five years, compared to more than half of heart transplant recipients who live over a decade. The poor long-term survival often stems from chronic rejection, which scars the lungs and has no effective medical treatment once it develops.
The key to Vallabhajosyula's breakthrough lies in small extracellular vesicles (sEVs)—tiny packages of biological molecules that cells release to communicate with one another. His team discovered that sEVs from T cells, the primary immune cells driving rejection, show measurable changes when acute rejection occurs. The challenge was immense: a single blood sample contains sEVs from virtually every cell type in the body, meaning T cell vesicles represent less than 1 percent of the total. To solve this, the researchers developed novel technology capable of extracting and enriching T cell sEVs specifically.
The team first validated their approach in mouse models of lung transplantation. Seven days after transplant, they compared sEV profiles from animals experiencing rejection against those without it, finding that the molecular patterns of rejection correlated with actual tissue damage in the lungs. Encouraged by those results, they tested the technology on 20 patients who underwent bilateral lung transplantation, analyzing blood samples collected at one, three, and 30 days post-surgery. The findings were striking. "The signals were dramatically different between those two groups," Vallabhajosyula says. "This is our first validation in humans that our T cell sEV data correlated perfectly with the biopsy data."
This work builds on momentum Vallabhajosyula's lab created last year when they developed a nearly identical blood test using T cell sEVs to detect acute rejection in heart transplant patients—suggesting the platform's potential extends across organ types. For lung transplant recipients, catching rejection earlier through a simple blood draw rather than risky surgery could be transformative. Early detection allows doctors to intervene when less damage has occurred to the organ, potentially reducing the likelihood that patients develop chronic rejection and improving long-term survival rates.
The researchers acknowledge that what they've accomplished so far is validation in a small patient population, but the implications are substantial. At a time when transplant shortages mean organs are precious and recipients are carefully selected, a noninvasive monitoring tool could mean the difference between detecting a treatable problem and losing a transplanted lung to progressive, untreatable scarring. As Vallabhajosyula notes, "We could very well be on our way to having a novel blood test that can replace or minimize having to do biopsies for lung transplant monitoring." For patients who have already survived the surgery and the long wait, that would be a welcome reprieve.