Monocyte-derived macrophages contain persistent latent HIV reservoirs, Veenhuis, et Al, 2023

https://www.nature.com/articles/s41564-023-01349-3

The development of persistent cellular reservoirs of latent human immunodeficiency virus (HIV) is a critical obstacle to viral eradication since viral rebound takes place once anti-retroviral therapy (ART) is interrupted. Previous studies show that HIV persists in myeloid cells (monocytes and macrophages) in blood and tissues in virologically suppressed people with HIV (vsPWH). However, how myeloid cells contribute to the size of the HIV reservoir and what impact they have on rebound after treatment interruption remain unclear. Here we report the development of a human monocyte-derived macrophage quantitative viral outgrowth assay (MDM-QVOA) and highly sensitive T cell detection assays to confirm purity. We assess the frequency of latent HIV in monocytes using this assay in a longitudinal cohort of vsPWH (n = 10, 100% male, ART duration 5–14 yr) and find half of the participants showed latent HIV in monocytes. In some participants, these reservoirs could be detected over several years. Additionally, we assessed HIV genomes in monocytes from 30 vsPWH (27% male, ART duration 5–22 yr) utilizing a myeloid-adapted intact proviral DNA assay (IPDA) and demonstrate that intact genomes were present in 40% of the participants and higher total HIV DNA correlated with reactivatable latent reservoirs. The virus produced in the MDM-QVOA was capable of infecting bystander cells resulting in viral spread. These findings provide further evidence that myeloid cells meet the definition of a clinically relevant HIV reservoir and emphasize that myeloid reservoirs should be included in efforts towards an HIV cure.
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Despite these limitations, we provide evidence that monocytes from long-term vsPWH contain persistent latent HIV that upon reactivation is replication-competent and capable of viral spread. This study provides direct evidence that monocyte reservoirs should be included in HIV cure efforts.

https://doi.org/10.1038/s41564-023-01349-3

 

Of potential relevance to LC given the finding of spike protein in (non-classical) monocytes out to 16 months from infection. SARS-CoV-2 in myeloid precursors sounds like something worth checking for.

 

There is something peculiar about the way this group describes the cell populations - as if they don't really understand the cell life history.

As far as I can see their 'monocyte-derived-macrophages are monocytes that they turn into macrophages in their assay system. So the population in vivo is monocytes. There is no 'MDM reservoir'. I am not aware that monocytes ever travel into tissues and then return to blood as monocytes. So their second hypothesis seems to be a misunderstanding.

The spleen has no real vascular barrier so in a sense is part of the blood compartment, but lymph node is more similar to other tissues.

Monocytes are cells designed to pick up rubbish so it is not surprising they contain some viral material. I can see that it might be important if been marrow myeloid precursors were a reservoir of viral DNA, but why not make that the topic of the paper?

 

Additional to Hutan's comment above.

I was confused by their use of the term ''monocyte-derived macrophages". The first Google hit was from Monocyte isolation techniques significantly impact the phenotype of both isolated monocytes and derived macrophages in vitro (2020, Immunology). The first line said —

Which suggests the term might be confined to the investigative technique. But this paper uses the term for in vivo macrophages. Presumably the term has been broadened in order to draw a distinction with tissue-resident macrophages.

From Tissue-specific macrophages: how they develop and choreograph tissue biology (2023, Nature Reviews Immunology) —

See also —

Tissue-Resident Macrophage Ontogeny and Homeostasis (2016, Immunity)
The development and maintenance of resident macrophages (2016, Nature Immunology)

 

I am pretty sceptical about all this 'non-classical monocyte' stuff. People love to invent these terms but often with very limited knowledge of both histology and haematology. I published on the distribution of CD16+ macrophages in human tissues with Ajay Bhatia back in 1998. At that time some other subsetting was popular.

I haven't looked at it in detail but there is difference between cells wandering through spleen, where there are no real vascular boundaries, and setting up in other tissues like skin and pericardium. CD16+ cells in these other tissues take on an extended macrophage cytoplasm and position themselves in very specific microenvironments. I find it hard to believe that they then get rid of all the cytoplasm and return to 'monocyte' morphology in which much of the cell is nucleus. Anything bigger than that would not go through capillaries - which is why all white blood cells are compact.

 

That looks like a typical promotional review by people who haven't bothered to read literature from forty years earlier! The complexity of macrophage behaviour was known to people like Wally Spector and Ralph van Furth in 1980. And mice are often very different from men.

 

[Off topic!] Interested in your views re this research -
https://news.cornell.edu/stories/2023/04/95m-fund-chronic-fatigue-syndrome-research

 

Is the idea being proposed that they don't become macrophages with macrophage morphology, but that they are still monocytes (briefly) in tissue, without time to further differentiate and increase cytoplasm and contents?

The reference Hutan noted above is Circulatory and maturation kinetics of human monocyte subsets in vivo (2017) and has only been cited 4 times since. But to (hopefully correctly) summarise the proposed concept —

Monocytes can be subclassified based on their surface markers, particularly CD16 and CD14. Three subtypes seem popular in the literature, eg Nomenclature of monocytes and dendritic cells in blood (2010, Blood).

Classical (CM): CD14Hi CD16Lo
Intermediate (IM): CD14Hi CD16Dim
Non-Classical (NCM): CD14Dim CD16Hi

Then they say that these subsets differentiate in a linear fashion:

CM -> IM -> NCM

They then propose - by fitting to a model to explain observations relating to deuterium-labelled glucose - that IMs might spend time in tissue.

CM -> IM -> IM (briefly in tissue, but still monocyte morphology) -> NCM

So if the potential for a detour into tissue were valid, what's the purpose?

From Gene expression profiling reveals the defining features of the classical, intermediate, and nonclassical human monocyte subsets (2011, Blood) —

Perhaps IMs can briefly scavenge from tissue and present antigens back in the blood, where they might affect eg circulating T cells etc?

 

All you need to do to make a CD14+ CD16- monocyte into a CD14low/CD16high monocyte is sit them on plastic for a day or two, as Vicki Abrahams did in my lab. Calling these 'subsets' is popular with people with pigeonhole minds but obscures the dynamics.

 

Thanks for clarifying. So to attempt to summarise this aspect for the thread and I hope I'm following you correctly —

Publications and indeed professional orgs seem to have settled on the idea of monocyte subsets, principally on the basis of the observed CD14/16 surface markers. Further work then tries to demonstrate and explain functional differences and maturation/differentiation based on the idea that there are these subsets.

However, this is simplistic and in the real world of experienced immunology observations, this might be more of a spectrum and it's clear that monos can - let's call it - "swap priority expression of 14 vs 16" (possibly in either direction?). A '14' can be triggered into a '16' pretty easily and even just with time, while leaving them alone in vitro. So, it's not especially important to the understanding of monocyte functions to over-emphasise the 14 vs 16 aspect, and it might be better if we simply look at them as a somewhat heterogeneous group of monocytes.