INTRODUCTION
INKmune is an NK cell based drug candidate for hematological and solid tumors, which – insofar as we see it - comes with the advantages of NK cell therapy without its limitations. It has a much lower production cost and is much more easily scalable than other drug candidates that we are aware of. We consider the technique of using a cell line to prime NK cells to be unique compared to the other drug candidates in the immune-oncology space we are aware of.
This part of the series takes a deeper dive into the mechanism of action (MoA) of INKmune, apologies in advance for its technical character. It is based on a long interview your humble servant had the chance to have with the man behind INKmune, Prof. Mark Lowdell, on 8 December 2021, excerpts of which will be included throughout the below text. That interview had been preceded by the typical forward-looking statements. Apologies in advance if it's a lot to digest at once. I assure you it was no different for me.
NK cell evasion by cancer cells
Cancer is essentially a disease of the failing immune system. The overall response of an NK cell depends on the balance of different stimulatory and inhibitory receptors and molecules. Tumors evade the immune system by making that balance turn out in their favor. The picture below shows some of the recurring receptors/cytokines at play in NK cells:
- left: inhibitory receptors such as NKG2A and killer immunoglobulin-like receptors (KIRs) bind to HLA ligands to inhibit NK cells;
- right: NKG2D detects proteins from MIC and ULBP families on the surface of malignant cells to eliminate such cells;
- right: IL-15 is a cytokine that activates and stimulates NK cells (like IL-12 and IL-18);
- right: CD16 triggers antibody-dependent cellular cytotoxicity.
- not shown here but worthy of note: NKp80 is a triggering molecule, CXCR4 is associated with migration of the NK cells from the periphery into a tumor (‘diapedesis’), and CD3ζ is a further important molecule for NK cell activation.
Evasion by cancer cells of NK cell immunosurveillance can occur by different mechanisms, such as:
o upregulating inhibitory signaling, e.g. by expressing HLA molecules to activate KIRs or upregulating HLA-E;
o suppressing activation signaling, by e.g. shedding of MICA and MICB or secretion of cytokines to block IL-12 or other cytokines such as IL-15 or IL-18.
The goal of an immuno-oncology drug candidate should then be to overcome this evasion.
The problems
In tumors that evade NK immunosurveillance (NK-resistant tumors), NK cells only kill tumor cells after having been activated by cytokines such as IL-2, IL-12, IL-15, or by cancer binding antibodies such as Rituximab or Herceptin. None of the cytokines which activate NK cells are specific to NK cells. The risk of off-target effects is very significant, as seen in the early IL-2 and IL-12 trials. Also, adding ‘cytokine support’ such as IL-15 could lead to long-term persistence problems due to ‘exhaustion, anergy or senescence’ of the NK cells: diminished signaling, decreased function, and ultimately reduced tumor control.
Although NK cells prove non-toxic and safe regardless of the cell numbers injected, there is often little persistence and expansion observed in a patient, which is vital for mounting an effective cellular response. Modern cancer therapy can eliminate most but not all cancer cells. The difference between survivors and relapsers (40/60% in the case of AML) is the patient’s immune system. The failure of the immune system to eliminate residual disease is the cause of the cancer relapse.
The drug candidate landscape in NK adoptive cell transfer therapy
As mentioned, NK cell based therapies may overcome many of the limitations/problems related to T-cell therapies, such as toxicity issues or graft-versus-host disease. The following overview of Nkarta shows where CAR-NK cell therapies rank:
The MoA of many NK-based drug candidates relates to one or more of the afore-mentioned proteins, cytokines and/or receptors. One could, for example, prevent shedding of MICA and MICB, or maintain NKG2D stimulation, or enhance IL-12, IL-15 or IL-18 expression. There are different ways to achieve those goals.
The competing immuno-oncology constructs we are aware of add different elements to an existing cell that has been activated and proliferated ex vivo. In an example below from Celyad oncology, one sees the CAR itself, a selection marker, add-ons such as cytokines, antibodies or receptors, and some further shRNA edits.
An example from Nkarta shows a CAR with an OX40 costimulatory domain, CD3ζ signaling, and membrane bound IL-15:
For allogeneic therapies (allogeneic meaning: not originating from the patient), different cell lines are used. Fate Therapeutics, Century Therapeutics, Cellectis, Cytovia, Editas Medicine, Exacis Biotherapeutics, Hebecell, Shoreline Biosciences, for example, use induced pluripotent stem cells. An advantage of such cells is their potential for infinite proliferation, yet that could be double-edged sword, as there may be heightened risks of development of tumors for multiple reasons (immature cells are retained in the final cell products, reprogramming factors remaining active or genetic mutations having occurred during in vitro culture).
Some of the further downsides to these therapy candidates are:
- proliferating, activating and constructing these adapted cells is costly, complex and time-consuming;
- the necessity of cryopreservation at -180° C and freeze/thaw issues;
- a rather quick loss of function in vivo post-adoptive transfer has been noted in many trials so far have, yielding relatively disappointing results in contrast to in vitro results; stimulation or activation ex vivo could create a state of dependence of the NK cells; exhaustion, anergy of senescence.
The MECHANISM OF ACTION OF INKmune
INKmune is an existing inactive tumor cell line that has been made replication incompetent that primes NK cells, but fails to trigger killing (lysis). INKmune expresses, among others, CD2 which binds to CD15 on the NK cells to trigger activation. Lysis then only occurs when the primed NK cells comes into contact with a tumor cell that had up to that point evaded the immune system. The professor explains all of that in more detail below. Note: K562 and RAJI are both tumor cell lines, but K562 is NK-sensitive and RAJI is NK-resistant.
INKmune does not expand, modify or activate NK cells like one sees in other immuno-oncology drug candidates.
What does it do then? In fact, a whole lot more than your regular CAR- or other construct, but it essentially provides the right signaling for the NK cell to kill a tumor cell when it comes into contact with one, and it leads to proliferation of NK cells in vivo.
INKmune activates over 600 genes which are critical to NK killing, and crosstalk with the adaptive immune system (among others T-cells).
Critical, here, seem to be CXCL10, STAT5B, CD70 and CXCR4 as mentioned above (for diapedesis – migration of NK cells into the tumor). Note: INB16 is INKmune.
In relation to stimulatory and inhibitory receptors on NK cells, INKmune results in, among others, upregulation of (stimulatory) NKG2D, downregulation of (inhibitory) NKG2A, upregulation of (triggering) NKp80, upregulation of CXCR4 (diapedesis) and upregulation of (activating) KIR3DL-1.
INKmune works
A powerful ‘pseudokine’™
INKmune converts resting NK cells to ‘primed’ NK cells (pNK) that are ready to start killing cancer cells once they come in contact with them. The immune synapse formed by INKmune is very strong, which allows the NK cells to deliver the lytic payload and death receptor signals to cancer cells which are resistant to resting NK cells.
It is for these reasons that INmune Bio refers to INKmune as a ‘pseudokine’™, and considered that no single cytokine has such broad physiological effects on NK cells compared to INKmune-primed NK cells. INKmune induces substantial killing, proliferation of NK cells and comes with no toxicity or dosage issues. Yet, the market has yet to discover that.
…with strong tumor ‘avidity’
In the framework of the upcoming ovarian cancer trial, INmune Bio has tested the avidity of NK cells to kill tumor cells, or the force by which ‘primed’ NK cells bind to ovarian tumor cells, as compared to resting NK cells, NK cells activated with IL-2 and NK cells activated with IL-15. This is important, I believe, as these cytokines are used by other competitors in the field.
And the results are pretty impressive, as INKmune shows a significantly stronger bond compared to any of the above:
TpNK cells are cells primed by INKmune. I’ll let the Professor do the rest of the talking here.
…which changes the phenotype of NK cells into memory-like NK cells
The company believes that this is the first ever successful generation of mlNK cells in patients.
This is huge news, which I believe has been missed by the market.
As mentioned in the previous blog post, NK cells were originally considered not to be able to behave in a memory-like manner, contrary to T-cells. This has been proven to be incorrect. A memory-like NK cell is an NK cell that has changed its phenotype from an NK cell in resting state, to an NK cell in a memory-like state with enhanced cancer-killing function. Memory-like NK cells are trending among NK scientists. Century Therapeutics has many ongoing trials with memory-like NK cells, and others do too.
INmune Bio reported over 50% of the expanded NK cells having an activated profile (CD69+/CD25+) on days eight and 15 of treatment, with a further increase to over 70% by day 29. More than 80% of the activated NK cells expressed markers associated with a memory-like NK cell (CD57++, NKG2D+, NKG2A-ve, NKp46-ve). In vitro, the INKmune™ activated NK cells were better at killing cancer cells than the patient’s own NK cells prior to treatment, with an 82% increase in lysis of K562 leukemia cells and a 47% increase in lysis of NK-resistant RAJI lymphoma cell tumor cells as early as day eight. Despite this high level of activated NK cells and tumor killing, the patient showed no symptoms of Cytokine Release Syndrome (CRS).
….showing considerable proliferation of NK cells in vivo
INKmune led to doubling of the number of peripheral blood NK cell numbers on day 8, as also reported by INmune Bio on 25 August 2021.
This news is far from little, as it shows the immune system’s activation, and renders proliferation of NK cells ex vivo (as in the other drug candidates) unnecessary.
…with remarkable persistence
INKmune also shows remarkable persistence. In its first patient, INKmune presents these results, with day 119 the last time point measured:
That is 17 weeks on no cytokine support. For clarity, the above is a chart I have drawn up, combining the information from two press releases.
For reference:
- Fate Therapeutics reported on 15 September 2021 that its CAR-NK drug candidate FT538 “persists in vivo at high levels for more than six weeks in the absence of cytokine support after adoptive transfer, whereas adoptively-transferred peripheral blood NK cells required the co-infusion of either IL-2 or IL-15 to achieve low-level persistence for up to two weeks.”
That’s six weeks of persistence compared to 2 weeks. That drug candidate is the an ‘off-the-shelf, multiplexed-engineered, iPSC-derived NK cell product candidate, with as novel engineered components, the knockout of CD38 and the expression of IL-15/IL-15R fusion protein.’
In my view, INKmune seems to outperform that persistence problem, by far. Yet, I do not believe the market has seen that.
Lowering a patient’s ECOG score
Does it work? In the first patient treated in the official trial, an elderly patient has seen his ECOG score go from 2 to 0, which appears to be exceptional, ‘unseen’ even, in such a patient).
The first patient under the compassionate use program, a young girl who had refused her transplant and had little chance of survival in the short term, has been given a triple dose of INKmune, and has been able to go home soon after. She seems to be able to bridge the gap to a second transplant, which could cure her. For clarity, compassionate use cases are not official trial cases. It concerns patients who have no further treatment options at their disposal, with very low chances of survival in the short term. The first patient’s official trial has ended, but if he would regress at this point, he could also be treated under the compassionate use program.
Reduced cost and scalability
It has been explained how costly and time-consuming that whole process is. Plus, complex processes require complex manufacturing and come with scalability issues.
INKmune does not come with all those hurdles.
Setting expectations right
INKmune has been designed to work in tumors that can be killed by NK cells.
INKmune’s Phase 1 trial is an all-comer trial; there is no patient screening and selection in advance, which should be different in a phase 2 trial. No cancer therapy is effective in each and every patient, and that can be for a variety of reasons: the level of the patient’s immune response, the cancer cells present in his body, etcetera. This also goes for any NK immunotherapy. One can therefore not expect, at this stage, that all patients will respond to treatment. There may be patients with tumors or NK cells that INKmune will not work in.
As an example, the antigen CD-19 in B-cell malignancies was the first tumor antigen targeted with this approach, and became the first approved therapeutic. 60% of patients with B-cell lymphomas are resistant to treatment with CD19 CAR T-cells. Complete remission (CR) has been observed ranging from 70% to 90% in patients with resistant and released acute lymphoblastic leukemia, and 57% in patients with end-stage advanced CLL. Despite high remission rates, 50% of patients with B-cell acute lymphoblastic leukemia (B-ALL) treated with CAR T-cells for CD19 and CD22 eventually relapse, due to lack of persistency of the therapy.
Responders are those that respond to treatment, but how strong that response is, is also important. A complete remission is a disease state where all signs of cancer in response to treatment have disappeared, but that does not always mean the cancer is fully gone.
A patient can relapse after initial therapy, and INKmune was designed to treat residual disease after such therapy, so as to prolong the time of survival. If the results so far continue, one could consider a combination therapy from the start of diagnosis (or perhaps even a standalone therapy, who knows).
Conclusion
INKmune induces substantial killing of tumor cells, profileration of NK cells, and comes with no toxicity or dosage issues. It has more broad physiological effects on NK cells compared to any other existing drug candidate. It is effortlessly cheaper and more scalable.
INKmune-primed NK cells show avidity far beyond those treated with IL-2 or IL-15. The immune synapse it produces, which was lacking prior to treatment, is remarkably strong.
INKmune’s persistence is off-the-charts,
If we look at INKmune, we believe Nkarta’s slide above should then come with an addition for INKmune:
To me, that looks like INKmune could be ahead of the field, but don’t take it as investment advice. And with all of the recent tax-loss-related or other selling of late, you get all of this, including XPro, for the beautiful price of $ 184 million. Winter sales have come a month ahead of time.
That rounds up my review of INKmune. I expect to publish about three more parts to this series, for the time being. This series can then serve as the foundation for future articles or videos to a wider audience.
Happy 2022 !