MLR’s are performed to assess whether T-cell proliferation is increased or inhibited in response to cellular or other external stimuli. Simply stated, an increase in proliferation indicates an increase in T-cell response to the test article, whereas an inhibited cell proliferation indicates a decrease in T-cell response to the test article. Therefore, the proliferative response is a functional test which demonstrates how the T-cell is affected by the test article.
MLR’s can be very adaptable in that they can be tailored to answer a specific immunological question by changing the MLR format (one-way versus two-way), changing the types of cells used, and choosing appropriate readouts. However, there are two basic reasons as to why we would want to perform an MLR. First, the MLR is a useful in-vitro model of the adaptive immune system and as such we can test new immunotherapies (drugs, biomaterials, etc) to see how they can enhance, suppress, or otherwise alter immune function. Second, MLR’s test how likely a new immunotherapy is to cause an unwanted immune response (immunogenicity). Because the MLR uses cultured immune cells, we can test the safety and efficacy of new therapies in a cell culture prior to moving forward with clinical trials.
In the field of immuno-oncology, an MLR can be used to model certain cancer states and evaluate how effective a new therapy is. Cancerous tissues and cells are well known for their ability to suppress our body’s immune system or otherwise “trick” our immune systems into not recognizing them as threats to be eliminated. Cancer researchers are developing a wide range of new therapies that utilize many different approaches, all with the common goal to recover and enhance our bodies suppressed immune system to recognize and eliminate cancerous growths. Using an MLR we can approximate these suppressed immune states (such as a T-cell exhaustion assay) to investigate how we can recover function (immune-checkpoints) or outright eliminate cancerous cells (such as with CAR T-cells) in a Mixed Lymphocyte Tumor Cell Assay (MLTuC).
In regenerative medicine, MLRs can be used to assess how effective a treatment is at suppressing an unwanted inflammatory response (such as towards damaged tissue) and begin to promote wound repair and healing. By tailoring the readout method used for MLR’s, we can observe the reduction in pro-inflammatory cellular signals and can even monitor the activity of cells that take part in the immunosuppressive and repair process, such as regulatory T cells (Treg) and M2 macrophages.
Lastly, in transplant immunology, we often want to be able to determine if an implantable device, biomaterial, tissue scaffold, or cellular therapy is safe to transplant into a patient. In these MLR assays we co-culture immune cells from a human donor with the therapeutic product to observe if the product causes an unwanted immunogenic reaction.
Now that we’ve established what a MLR is, and why it would be performed, let’s take a closer look at how they are performed in the laboratory.