Hoxb4 overexpression in CD4 memory phenotype T cells increases the central memory population upon homeostatic proliferation.

Memory T cell populations allow a rapid immune response to pathogens that have been previously encountered and thus form the basis of success in vaccinations. However, the molecular pathways underlying the development and maintenance of these cells are only starting to be unveiled. Memory T cells have the capacity to self renew as do hematopoietic stem cells, and overlapping gene expression profiles suggested that these cells might use the same self-renewal pathways. The transcription factor Hoxb4 has been shown to promote self-renewal divisions of hematopoietic stem cells resulting in an expansion of these cells. In this study we investigated whether overexpression of Hoxb4 could provide an advantage to CD4 memory phenotype T cells in engrafting the niche of T cell deficient mice following adoptive transfer. Competitive transplantation experiments demonstrated that CD4 memory phenotype T cells derived from mice transgenic for Hoxb4 contributed overall less to the repopulation of the lymphoid organs than wild type CD4 memory phenotype T cells after two months. These proportions were relatively maintained following serial transplantation in secondary and tertiary mice. Interestingly, a significantly higher percentage of the Hoxb4 CD4 memory phenotype T cell population expressed the CD62L and Ly6C surface markers, characteristic for central memory T cells, after homeostatic proliferation. Thus Hoxb4 favours the maintenance and increase of the CD4 central memory phenotype T cell population. These cells are more stem cell like and might eventually lead to an advantage of Hoxb4 T cells after subjecting the cells to additional rounds of proliferation

Expression of Heme Oxygenase-1 in Neural Stem/Progenitor Cells as a Potential Mechanism to Evade Host Immune Response

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Change of naïve and MP T cell populations in <i>Hoxb4</i> transgenic and wt mice with age.

<p>Scatter plots showing the percentage of (<b>A</b>) CD4 and (<b>B</b>) CD8 T cells that are naïve (CD44^lo/CD62L^hi), MP (CD44^hi) or are a subpopulation of MP T cells (CD44^hi/Ly6C^hi) for LN, Spl and BM derived from individual <i>Hoxb4</i> transgenic and wt (n = 6–8) age matched mice. Young mice are between 3–4 months and old mice are all older than 28 months. Naïve and MP populations change significantly with age, but not between <i>Hoxb4</i> and wt mice. *P<0.05, 2-tailed Student ttest. MP = memory phenotype, Wt = wild type, LN = lymph node, Spl = spleen and BM = bone marrow.</p

Competitive short-term homeostatic proliferations (7 days) of <i>Hoxb4</i> transgenic and wt CD4 MP T cells.

<p>(<b>A</b>) Scheme of the experimental approach. CD4 MP T cells are sorted from CellTrace™ Violet (CTV) labelled cells isolated from LN and Spl of <i>Hoxb4</i> (CD45.1/2) and congenic wt (CD45.1) mice. Cells of both genotypes are transplanted in a 1∶1 ratio in CD3ε^−/− (CD45.2) mice. (<b>B</b>) FACS profiles showing <i>Hoxb4</i> and wt fractions to donor derived CD4 MP T population (CD45.1) in LN (left panel). Representative FACS profiles for CD62L and CTV on <i>Hoxb4</i> and wt populations. Loss of CTV tracer indicates that most cells are dividing rapidly (right panels). (<b>C</b>) Average contribution (%) of <i>Hoxb4</i> and wt cells to donor derived MP T cells in LN, Spl and BM (n = 3). (<b>D</b>) Percentage of CD62L^hi MP T cells in <i>Hoxb4</i> and wt population found in lymphoid organs. *P<0.05; paired 2-tailed Student ttest. Wt = wild type, MP = memory phenotype, LN = lymph node, Spl = spleen and BM = bone marrow.</p

Total donor cells contribution to hematopoietic organs and the proportion of <i>Hoxb4</i> versus wild type cells.

<p>LN = Lymph node; BM = bone marrow, wt = wild type.</p

Percentage of T cell populations in hematopoietic organs of young adult mice.

<p>Note that no significant differences were observed between T cell populations of <i>Hoxb4</i> and wild type mice. 1-tailed Student ttest, comparing <i>Hoxb4</i> vs. wild type mice. LN = Lymph node; BM = bone marrow.</p

Medium-term competitive homeostatic proliferations (60 days) of <i>Hoxb4</i> transgenic and wt CD4 MP T cells.

<p>(<b>A</b>) FACS profile showing fractions of <i>Hoxb4</i> and wt cells to donor derived MP T population in lymph node (LN). (<b>B</b>) Stacked bar graphs indicating the average contributions of <i>Hoxb4</i> and wt cells in LN, Spl and BM measured in three independent experiments; n = 9. (<b>C</b>) FACS profiles for the expression of typical memory T cell surface markers on <i>Hoxb4</i> and wt MP T cells in the BM. (<b>D</b>) Average subpopulations of <i>Hoxb4</i> and wt MP T cells expressing the indicated surface markers in LN (upper panel), Spl (middle panel) and BM (lower panel). (<b>E</b>) Percentage of <i>Hoxb4</i> and wt MP T cells (gated on CD44^hi) positive for indicated cytokines (n = 3–6). *P<0.05, 2-tailed Student ttest. MP = memory phenotype, wt = wild type, LN = lymph node, Spl = spleen and BM = bone marrow, TNF = tumor necrosis factor; IL-2 = interleukine-2; IFN = interferon.</p

Long-term competitive homeostatic proliferations (180 days) of <i>Hoxb4</i> transgenic and wt CD4 cells.

<p>(<b>A</b>) Scheme of serial transplantations. 10×10⁶ cells of the LNs of primary hosts that received a transplant composed of equal doses of <i>Hoxb4</i> and wt MP T cells were serially transplanted into secondary and tertiary hosts with a 60 days interval. (<b>B</b>) Compilation of <i>Hoxb4</i> and wt fractions of donor derived cells in LN, Spl and BM of secondary (n = 6) and tertiary hosts (n = 4) from two independent experiments. (<b>C</b>) Bar graphs showing the average percentage of cells positive for CD62L and Ly6C within the <i>Hoxb4</i> or wt memory T populations. *P<0.05, 2-tailed Student ttest. Wt = wild type, MP = memory phenotype, LN = lymph node, Spl = spleen and BM = bone marrow.</p