First, an explanation of why poison ivy gives you a rash. Poison ivy contains an oil called urushiol. Get this on your skin and it diffuses through the skin layers. Interspersed in these skin layers are white blood cells called Langerhans cells that normally reside in the skin to help prevent infection. Urushiol binds to Langerhans cells by attaching to a receptor on their surface called CD1a. This binding attracts the interest of another type of white blood cell, the T lymphocyte, known for its ability to release substances that cause intense inflammation. Hence, the annoying, itchy rash of poison ivy.

How can we harness this effect to treat cancer?

As discussed in my last post, immunotherapy is the biggest advance in the treatment of cancer in decades. Immunotherapy is an intravenous medication given every few weeks that releases the block that prevents T lymphocytes from killing cancer cells. Much research now focuses on maximizing their potential. T lymphocytes are fickle, and may or may not decide to infiltrate into cancerous growths. Cancers infiltrated with T lymphocytes are called hot tumors and cancers devoid of T lymphocytes are called cold tumors. Whether a cancer is infiltrated with T lymphocytes has become increasingly relevant, because immunotherapy is more effective when treating hot vs cold tumors.  Much research is now focused on converting tumors from cold to hot.

Next, we turn our attention to Langerhans cells. Cancers, especially metastatic skin cancers, are often infiltrated with Langerhans cells. Metastatic skin cancers are also now treated with immunotherapy. Unfortunately, response rates are only as high as 30 to 40%, but often dramatic when they occur.

This raises the question: could urushiol be given along with immunotherapy intravenously to bind to Langerhans cells, thus recruiting more T lymphocytes to the cancer and converting a cold tumor to a more treatable hot tumor? Furthermore, could urushiol and immunotherapy be used to treat a variety of disorders where Langerhan cells are pathologically overproduced in the body (histiocytic diseases)?

Just speculation of course. There are some recent small studies looking at urushiol as a cancer treatment, but its real potential may be in conjunction with immunotherapy!