A variety of floridly paranoid conspiracy theories posit that plans are afoot to tag people with barcodes to track their movements. In the current issue of the Journal of Experimental Medicine, Koen Schepers and colleagues show that barcode surveillance can be employed for a more benign purpose. The study uses a technique called molecular barcoding to track the CD8 T cell response to infections, in order to investigate the extent to which the site of initial activation influences the trafficking of antigen-specific effector cells.
The researchers used a dual challenge model in which mice infected intranasally with influenza encoding one type of ovalbumin (OVA) antigen and a day later tumor cells encoding a different OVA antigen were injected subcutaneously. Two sets of CD8 T cells specific for each OVA antigen were transferred into the mice prior to challenge, each set tagged with molecular barcodes that could be identified using polymerase chain reaction (PCR) and microarray analyses. Five days after challenge, tagged CD8 T cells were largely localized to the lymph node draining the site of exposure (the lung-draining mediastinal lymph nodes and tumor-draining axillary/linguinal lymph nodes, respectively). But within 6-8 days post-challenge, the authors noted that a marked shift occurred and CD8 T cells containing different barcodes became intermingled in both sets of lymph nodes, indicating that proliferation had led to extensive systemic distribution of the responding cells.
To investigate whether the findings held true for the gut, an experiment was conducted using oral infection with listeria moncytogenes instead of influenza. In this case, there were mice that did show a biased accumulation of some listeria-specific CD8 T cells in the gut, suggesting that selective trafficking can occur under some circumstances. However, most of the antigen-specific CD8 T cells showed equal distribution at both sites.
Because these initial experiments involved a three day culture period to introduce the molecular barcodes, which might conceivably have affected trafficking properties, the researchers also developed a method to introduce the barcodes into thymocytes, to ensure that the resultant tagged CD8 T cells were naïve cells. Repeating the experiment using these naïve CD8 T cells produced very similar results. In discussing the results the authors state that: “collectively, these data indicate that after a brief period of local accumulation, the dominant pattern of accumulation at effector sites is aselective.” However, one question not answered by these data is whether the memory CD8 T cells generated by the challenge antigens show preferential migration to the site of initial activation when re-challenged; for researchers pondering whether vaccines need to induce memory responses capable of localizing at specific sites, this will be an important issue for future studies to address.
The Journal of Experimental Medicine, Vol. 205, No. 10, 2309-2318
Published online September 22, 2008
Koen Schepers1, Erwin Swart1, Jeroen W.J. van Heijst1, Carmen Gerlach1, Maria Castrucci3, Daoud Sie2, Mike Heimerikx2, Arno Velds2, Ron M. Kerkhoven2, Ramon Arens1, and Ton N.M. Schumacher1
1 Division of Immunology and 2 Central Microarray Facility, the Netherlands Cancer Institute, 1066 CX Amsterdam, Netherlands
3 Istituto Superiore di Sanità, 00161 Roma, Italy
T cells, as well as other cell types, are composed of phenotypically and functionally distinct subsets. However, for many of these populations it is unclear whether they develop from common or separate progenitors. To address such issues, we developed a novel approach, termed cellular barcoding, that allows the dissection of lineage relationships. We demonstrate that the labeling of cells with unique identifiers coupled to a microarray-based detection system can be used to analyze family relationships between the progeny of such cells. To exemplify the potential of this technique, we studied migration patterns of families of antigen-specific CD8+ T cells in vivo. We demonstrate that progeny of individual T cells rapidly seed independent lymph nodes and that antigen-specific CD8+ T cells present at different effector sites are largely derived from a common pool of precursors. These data show how locally primed T cells disperse and provide a technology for kinship analysis with wider utility.