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- APOBEC3G (1)
- Antigen CD28 (1)
- Graft versus host disease (1)
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Institute
Hematopoietic stem cell transplantation is a curative therapy for malignant diseases of the haematopoietic system. The patients first undergo chemotherapy or irradiation therapy which depletes the majority of tumour cells before they receive the transplant, consisting of haematopoietic stem cells and mature T cells from a healthy donor. The donor T cells kill malignant cells that have not been eliminated by the conditioning therapy (graft versus leukaemia effect, GvL), and, therefore, are crucially required to prevent relapse of the tumour. However, the donor T cells may also severely damage the patient’s organs causing acute graft versus host disease (aGvHD). In mice, aGvHD can be prevented by interfering with the co-stimulatory CD28 signal on donor T cells. However, experimental models using conventional CD28 knockout mice as T cell donors or αCD28 antibodies have some disadvantages, i.e. impaired T cell development in the thymus of CD28 knockout mice and systemic CD28 blockade with αCD28 antibodies. Thus, it remains unclear how CD28 co-stimulation on different donor T cell subsets contributes to the GvL effect and aGvHD, respectively.
We developed mouse models of aGvHD and the GvL effect that allowed to selectively delete CD28 on certain donor T cell populations or on all donor T cells. CD4+ conventional T cells (Tconv cells), regulatory T cells (Treg cells) or CD8+ T cells were isolated from either Tamoxifen-inducible CD28 knockout (iCD28KO) mice or their wild type (wt) littermates. Allogeneic recipient mice were then transplanted with T cell depleted bone marrow cells and different combinations of iCD28KO and wt T cell subsets. Tamoxifen treatment of the recipients caused irreversible CD28 deletion on the iCD28KO donor T cell population. In order to study the GvL response, BCL-1 tumour cells were injected into the mice shortly before transfer of the T cells.
CD4+ Tconv mediated aGvHD was efficiently inhibited when wt Treg cells were co-transplanted. In contrast, after selective CD28 deletion on donor Treg cells, the mice developed a late and lethal flare of aGvHD, i.e. late-onset aGvHD. This was associated with a decline in iCD28KO Treg cell numbers around day 20 after transplantation. CD28 ablation on either donor CD4+ Tconv cells or CD8+ T cells reduced but did not abrogate aGvHD. Moreover, iCD28KO and wt CD8+ T cells were equally capable of killing allogeneic target cells in vivo and in vitro. Due to this sufficient anti-tumour activity of iCD28KO CD8+ T cells, they had a therapeutic effect in our GvL model and 25% of the mice survived until the end of the experiment (day 120) without any sign of the malignant disease. Similarly, CD28 deletion on all donor T cells induced long-term survival. This was not the case when all donor T cells were isolated from wt donor mice. In contrast to the beneficial outcome after CD28 deletion on all donor T cells or only CD8+ T cells, selective CD28 deletion on donor CD4+ Tconv cells completely abrogated the GvL effect due to insufficient CD4+ T cell help from iCD28KO CD4+ Tconv cells.
This study demonstrates that therapeutic inhibition of the co-stimulatory CD28 signal in either all donor T cells or only in CD8+ T cells might protect patients from aGvHD without increasing the risk of relapse of the underlying disease. Moreover, deletion of CD28 on donor Treg cells constitutes a mouse model of late-onset aGvHD which can be a useful tool in aGvHD research.
Measles is an extremely contagious vaccine-preventable disease responsible
for more than 90000 deaths worldwide annually. The number of deaths has
declined from 8 million in the pre-vaccination era to few thousands every year due
to the highly efficacious vaccine. However, this effective vaccine is still unreachable
in many developing countries due to lack of infrastructure, while in developed
countries too many people refuse vaccination. Specific antiviral compounds are not
yet available. In the current situation, only an extensive vaccination approach
along with effective antivirals could help to have a measles-free future. To develop
an effective antiviral, detailed knowledge of viral-host interaction is required.
This study was undertaken to understand the interaction between MV and
the innate host restriction factor APOBEC3G (A3G), which is well-known for its
activity against human immunodeficiency virus (HIV). Restriction of MV
replication was not attributed to the cytidine deaminase function of A3G, instead,
we identified a novel role of A3G in regulating cellular gene functions. Among two
of the A3G regulated host factors, we found that REDD1 reduced MV replication,
whereas, KDELR2 hampered MV haemagglutinin (H) surface transport thereby
affecting viral release. REDD1, a negative regulator of mTORC1 signalling
impaired MV replication by inhibiting mTORC1. A3G regulated REDD1
expression was demonstrated to inversely correlate with MV replication. siRNA
mediated silencing of A3G in primary human blood lymphocytes (PBL) reduced
REDD1 levels and simultaneously increased MV titres. Also, direct depletion of
REDD1 improved MV replication in PBL, indicating its role in A3G mediated
restriction of MV. Based on these finding, a new role of rapamycin, a
pharmacological inhibitor of mTORC1, was uncovered in successfully diminishing
MV replication in Vero as well as in human PBL. The ER and Golgi resident
receptor KDELR2 indirectly affected MV by competing with MV-H for cellular
chaperones. Due to the sequestering of chaperones by KDELR2, they can no longer
assist in MV-H folding and subsequent surface expression. Taken together, the two
A3G-regulated host factors REDD1 and KDELR2 are mainly responsible for
mediating its antiviral activity against MV.