Immunological and clinical aspects of cell therapy in the treatment of aftereffects of craniocerebral injury

Clinical results of neurorestorative cell therapies and therapeutic indications according to cellular bio-proprieties

Cell therapies have been explored to treat patients with nervous diseases for over 20 years. Even though most kinds of cell therapies demonstrated neurorestorative effects in non-randomized clinical trials; the effects of the majority type cells could not be confirmed by randomized controlled trials. In this review, clinical therapeutic results of neurorestorative cell therapies according to cellular bio-proprieties or cellular functions were introduced. Currently it was demonstrated from analysis of this review that some indications of cell therapies were not appropriate, they might be reasons why their neurorestorative effects could not be proved by multicenter, randomized, double blind, placebo-controlled clinical trials. Theoretically if one kind of cell therapy has neurorestorative effects according to its cellular bio-proprieties, it should have appropriate indications. The cell therapies with special bio-properties is promising if the indication selections are appropriate, such as olfactory ensheathing cells for chronic ischemic stroke, and their neurorestorative effects can be confirmed by higher level clinical trials of evidence-based medicine.

Why is olfactory neuroepithelium?

Currently, most cellular therapeutic effects for nervous diseases cannot be proven in a multicenter, randomized, double-blind placebo-control clinical trials, except for a few kinds of cells such as olfactory ensheathing cells. These cells show significant improvements in functional recovery and quality of life for patients with chronic ischemic stroke. Also, olfactory neuron transplantation has promising neurorestorative effects on patients with vascular dementia. Human olfactory neuroepithelium can spontaneously and sustainably regenerate or produce new olfactory neurons and glial cell types for decades or a lifetime. The neurorestorative mechanisms of olfactory ensheathing cells are well known; however, little is known about the neurorestorative mechanisms of olfactory neurons. Therefore, I hypothesize that the neurorestorative mechanisms of olfactory neurons after transplantation: (1) can well migrate where they are needed and become local functional neurons, as they need to compensate or replace; (2) must be regulated by some special molecular factors to elongate their axons, modulate or direct synapses to correctly recognize and connect the target cells, and integrate functions. Based on olfactory neuroepithelium cells displaying the special characterization, neurorestorative mechanisms, clinical therapeutic achievements, and hypotheses of effective mechanisms, they (olfactory ensheathing cells and olfactory neurons) may be the most efficient instruments of neurorestoration.

Clinical neurorestorative cell therapies: Developmental process, current state and future prospective

Clinical cell therapies (CTs) for neurological diseases and cellular damage have been explored for more than 2 decades. According to the United States Food and Drug Administration, there are 2 types of cell categories for therapy, namely stem cell-derived CT products and mature/functionally differentiated cell-derived CT products. However, regardless of the type of CT used, the majority of reports of clinical CTs from either small sample sizes based on single-center phase 1 or 2 unblinded trials or retrospective clinical studies showed effects on neurological improvement and the ability to either partially or temporarily thwart the deteriorating cellular processes of the neurodegenerative diseases. There have been only a few prospective, multicenter, randomized, double- blind placebo-control clinical trials of CTs so far in this developing novel area that have shown negative results, and more clinical trials are needed. This will expand our knowledge in exploring the type of cells that yield promising results and restore damaged neurological structure and functions of the central nervous system based on higher level evidence-based medical data. In this review, we briefly introduce the developmental process, current state, and future prospective for clinical neurorestorative CT.