Property always NULL in Rest Api

I have the following entity:

public class EntityBase<T> where T : class
{
    [DataMember]
    public int CurrentItemCount { get; set; }

    [DataMember]
    public int ItemsPerPage { get; set; }


    [DataMember]
    public int StartIndex { get; set; }

    [DataMember]
    public int PageIndex { get; set; }

    [DataMember]
    public List<T> Items { get; set; }

    [DataMember]
    public T Item { get; set; }

    public EntityBase() { }}

I have this REST service:

public EntityBase<Person> GetPerson(PersonFilter personFilter)

That I call from an HttpClient:

public T GetPostSync<T, TR>(string requestUri, string entityId = null, TR filter = null) where TR : class where T : class
    {
        var uri = string.Format(requestUri, entityId);
        var responseMessage = _httpClient.PostAsJsonAsync(uri, filter).Result;
        responseMessage.EnsureSuccessStatusCode();

        if (responseMessage.Content == null)
            return default(T);

        return JsonConvert.DeserializeObject<T>(responseMessage.Content.ReadAsStringAsync().Result);
    }

When deserializar, the properties Items and Item, always returns me null.

Why?

Regards,